SEARCH

SEARCH BY CITATION

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

Passive-margin salt basins are classified as prerift, syn-stretching, syn-thinning, and syn-exhumation. Prerift salt, such as the Triassic Keuper in the Western Pyrenees, undergoes thick-skinned extension, first decoupled and then coupled, along with its substrate and cover. The base salt develops significant relief, is attenuated on the largest faults, and ends up distributed across the entire margin. Syn-stretching salt, such as along the Iberian and Newfoundland margins, is deposited during early rifting and is thus concentrated in proximal areas with variable thickness and extent, with decoupled and coupled thick-skinned deformation dominant. Syn-thinning salt, such as in the northern Red Sea, is also deposited during extension, with the base salt unconformably above proximal stretching faults but offset by distal thinning faults. Both thick-skinned and gravity-driven thin-skinned deformation occur, with the latter strongly influenced by the ramp-flat geometry of the base salt. Syn-exhumation salt, such as in the Gulf of Mexico and South Atlantic salt basins, is deposited as part of the sag basin with broad distribution and a generally unfaulted base. Conjugate syn-exhumation salt basins are originally contiguous, form partly over exhumed mantle on magma-poor margin segments, and are commonly flanked by magma-rich segments with volcanic highs (seaward-dipping reflectors) that isolate the salt basin from marine water. Salt tectonics is characterized by gravitational failure of the salt and overburden, with proximal extension and distal contraction, and the development of allochthonous salt that includes frontal nappes that advance over newly formed oceanic crust.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

Salt basins on passive margins are typically classified as prerift, synrift, or postrift (e.g. Jackson & Vendeville, 1994; Tari et al., 2003). Prerift salt is deposited prior to the first extension associated with margin development, synrift salt is deposited in active half-graben during extension of the continental crust, and postrift salt is deposited during thermal subsidence that follows extension. Because paired salt basins on conjugate margins are common, evaporite deposition is generally thought to predate oceanic spreading (e.g. Duval et al., 1992; Davison, 1999; Pindell & Kennan, 2007), so that the salt basin becomes separated into two basins and the distal salt margins originate as breakup edges. In contrast, several researchers have suggested that some passive-margin salt postdates initial, subaerial spreading, so that the conjugate basins were never connected and the distal margins represent depositional edges where the salt onlapped proto-spreading centres (Fonck et al., 1998; Jackson et al., 2000; Imbert & Philippe, 2005).

Margins are usually characterized as either magma-rich or magma-poor, also termed volcanic and non-volcanic, respectively. Magma-rich margins are distinguished by common onshore large igneous provinces, seaward-dipping reflectors (SDRs) in distal provinces, and prominent magnetic anomalies, and include portions of offshore Norway, the east coast of the United States, and the Pelotas and Walvis basins of the South Atlantic (e.g. Mutter et al., 1982; Planke et al., 2000; Talwani & Abreu, 2000; Geoffroy, 2005; Blaich et al., 2011). SDRs are nonexistent or poorly developed on magma-poor margins, which include those of Iberia, Newfoundland, NW Australia and the Labrador Sea (e.g. Karner & Driscoll, 2000; Whitmarsh et al., 2001; Manatschal, 2004; Reston, 2009; Péron-Pinvidic & Manatschal, 2010; Pérez-Gussinyé, 2013). Although it has been argued that the separation into magma-rich and magma-poor margins is too simplified (Manatschal & Karner, 2012; Péron-Pinvidic et al., 2013), the terminology remains in common use and will be applied here.

Studies of magma-poor passive-margin geometry and evolution have led in recent years to new geodynamic models (e.g. Whitmarsh et al., 2001; Lavier & Manatschal, 2006; Péron-Pinvidic & Manatschal, 2009; Reston, 2009; Huismans & Beaumont, 2011; Pérez-Gussinyé, 2013). These studies have made use of better seismic imaging (both reflection and refraction) of the crustal architecture of various margins, ODP wells in deepwater settings, numerical models, and outcrop studies in the Alps and Pyrenees (e.g. Lemoine et al., 1986; Froitzheim & Eberli, 1990; Florineth & Froitzheim, 1994; Manatschal, 2004; Jammes et al., 2010; Mohn et al., 2010). In particular, the conjugate margins of Iberia and Newfoundland have become the type area for magma-poor margins because of the wealth of excellent subsurface data (e.g. Boillot et al., 1987; Krawsczyk et al., 1996; Reston, 1996; Shillington et al., 2004; Van Avendonk et al., 2006; Ranero & Pérez-Gussinyé, 2010). Reflection and refraction seismic and multiple wells have demonstrated such features as continental crust less than 10-km thick, low-angle extensional faults, and an oceanic–continental transition zone more than 100-km wide comprising a mixture of thinned and rotated allochthons of continental crust, areas of oceanic crust, and blocks of exhumed, serpentinized subcontinental mantle.

Of the various published models, I focus here on the four-stage model for hyperextended, magma-poor margins of Péron-Pinvidic & Manatschal (2009) for the simple reason that it best explains the different types of salt basins on passive margins. Their model (Fig. 1) combines elements of early pure-shear extension (McKenzie, 1978) followed by simple-shear extension (Wernicke, 1981). In the stretching stage, the brittle upper crust is extended by steep, mostly planar ‘stretching’ faults, with deformation decoupled from that in the ductile middle to lower crust, which stretches and thins (Fig. 1a). Extension becomes more focused during the thinning stage, in which lower angle, inwardly dipping conjugate ‘thinning’ faults in the upper crust (which bound the common hangingwall, or H-block) and outwardly dipping conjugate faults in the stronger mafic lower crust and upper lithospheric mantle are decoupled by the middle crust (Fig. 1b). Once the middle crust is thinned enough, a low-angle detachment fault cuts the entire lithosphere; as the hanging-wall slides off the footwall; subcontinental mantle is exhumed beneath the detachment during the exhumation stage (Fig. 1c). Ultimately, complete breakup and accretion of oceanic crust marks the onset of the spreading stage (Fig. 1d). A more recent summary of this model subdivides the third stage into the hyperextension and exhumation phases, with the development of multiple low-angle faults that merge downward into a master detachment at the top of the mantle (Péron-Pinvidic et al., 2013).

image

Figure 1. Model of four-stage evolution of a magma-poor passive margin (modified from Péron-Pinvidic & Manatschal, 2009).

Download figure to PowerPoint

No single stage is necessarily linked to the development of a salt basin. Instead, evaporite deposition simply requires basin isolation, an arid climate, and an adequate supply of water (e.g. Warren, 2006). If the conditions are right, salt may predate extension or may theoretically form during any of the stages. In this article, I offer a new classification for passive-margin salt basins: prerift salt, syn-stretching salt, syn-thinning salt, and syn-exhumation salt. In the new formulation of the model (Péron-Pinvidic et al., 2013), syn-thinning would include salt deposited during hyperextension; in other words, syn-exhumation salt postdates brittle upper-crustal extension. Syn-spreading salt is not included because it is globally insignificant. I use the Péron-Pinvidic & Manatschal (2009) model (Fig. 1) as a template to show, for each type, the implications for evaporite deposition and subsequent salt tectonics, including diapir initiation, thick- and thin-skinned deformation, and allochthonous salt development. At least one example of each type of salt basin is proposed and discussed, and I suggest that the major Atlantic salt basins such as those in the South Atlantic and the Gulf of Mexico are syn-exhumation salt basins. I also evaluate the relationship of syn-exhumation salt basins to magma-poor and magma-rich portions of margins, the uplift and subsidence histories of margins, and the internal character of layered evaporite sequences.

Prerift Salt Basins

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

Model

Prerift salt is just another prerift stratal interval and thus subject to the total amount of extension. However, it is fundamentally different from other prerift strata because of its viscous behaviour. Jammes et al. (2010) proposed that the salt initially decouples deformation above and below, thereby preventing crustal detachments and subsalt material from emerging at the sea floor during early stages, but that subsequent faults cut through to the surface and basement may be exhumed after the salt is sufficiently thinned.

The initial spatial and thickness distribution of the salt is dependent on the pre-existing tectonic setting and topography at the time of evaporite deposition. Although there are certainly exceptions, relief on the base salt is generally minimal and there are only gradual, regional thickness changes (Fig. 2a). Salt mobilization and diapirism are triggered by thick-skinned extension during the stretching stage (Fig. 2b). The base salt is offset by high-angle normal faults, with the top salt and stratal cover forming drape folds over the basement-involved faults (Jackson & Vendeville, 1994). Initially, extension in the cover is typically decoupled by the salt and is manifested by the development of thinned-skinned normal faults and reactive diapirism, with increasing offset in the base salt forming basinward-dipping ramps in the décollement layer. The degree of decoupling is dependent on a number of variables (Jackson & Vendeville, 1994; Stewart & Clarke, 1999; Withjack & Callaway, 2000), of which the salt thickness and displacement magnitude are paramount. Thick salt, a high ratio of extension rate to sedimentation rate, and thin cover all favour the ultimate development of passive diapirs (Vendeville & Jackson, 1992a) generally located above or in the footwalls of underlying normal faults.

image

Figure 2. Model of prerift salt basin using template modified from Péron-Pinvidic & Manatschal (2009): (a) simple, constant-thickness prerift salt; (b) stretching stage with triggering of diapirism by thick-skinned extension; (c) thinning stage with continued diapirism and thin-skinned extension where thinning faults merge into salt décollement; (d) exhumation stage with only minor continued salt-related deformation; and (e) spreading stage showing salt distributed throughout margins.

Download figure to PowerPoint

Deformation gradually becomes more coupled as extension increases, so that the salt becomes highly attenuated or completely absent on thinning faults (Fig. 2c). Extension and thinning of the salt eventually inhibit further diapir growth, leading to diapir burial or even collapse (Vendeville & Jackson, 1992b). Salt tectonics is largely over by the mantle-exhumation stage (Fig. 2d), although thin-skinned gliding may continue where the salt or equivalent weld dips basinward due to differential subsidence. Some salt may be attached to crustal allochthons and thereby end up over serpentinized mantle. Ultimately, salt is distributed throughout the margin but is likely to be discontinuous in more distal areas due to extreme extension (Fig. 2e).

Example

A well known example of a prerift salt basin is the Upper Triassic Keuper salt along the northern margin of Iberia, both onshore in the Pyrenees and offshore in the eastern Bay of Biscay (Fig. 3). Upper Triassic salt has a widespread distribution from north-west Europe to north-west Africa, and is generally considered to have been deposited in a postrift setting related the earlier breakup of Pangaea (e.g. Ziegler, 1988; Dercourt et al., 1993), although there may have been local extension ongoing during early evaporite deposition. The salt is overlain by prerift carbonates of latest Triassic through Late Jurassic age that also had widespread distribution in northern Spain. Extension related to the opening of the Bay of Biscay began during the latest Jurassic (Ferrer et al., 2008; Jammes et al., 2009; Roca et al., 2011) and was focused in a series of east–west trending rift basins including the Basque-Cantabrian, Parentis, and Lacq-Mauléon basins (Fig. 3). In the Pyrenees and eastern Bay of Biscay, thinning began during the late Aptian and mantle exhumation started during the latest Aptian and continued through the Albian (Henry et al., 1998; Jammes et al., 2009; Roca et al., 2011). Spreading began during the late Albian to the west, but only exhumed mantle, which is exposed onshore in the Mauléon Basin (Fig. 3), formed to the east due to an eastward decrease in the total amount of extension.

image

Figure 3. Northern Iberian margin, an example of prerift salt: (a) map reconstruction of the Bay of Biscay and Western Pyrenees during the Cenomanian, at the end of rifting (modified from Roca et al., 2011), with lesser extension to east leading to mantle exhumation and greater extension to west resulting in oceanic spreading; (b) simplified cross-section through the Basque-Cantabrian and Parentis basins restored to the Cenomanian, before Pyrenean contraction (modified from Roca et al., 2011; (c) simplified cross-section through the Mauléon Basin restored to the Late Cretaceous, before Pyrenean contraction (modified from Jammes et al., 2010).

Download figure to PowerPoint

Salt movement was triggered by thick-skinned extension, with diapirs forming above or near underlying normal faults and commonly forming linear ridges (e.g. Ferrer et al., 2012). Cover extension was at least partly decoupled, with listric normal faults on the rift shoulder soling into the Keuper salt décollement and accommodating significant extension, resulting in gaps of up to 20 km in the prerift Jurassic. The Keuper salt was highly attenuated and/or offset on the major thinning faults. In more distal settings, the salt locally ended up directly in contact with underlying serpentinized mantle due to exhumation beneath the stretching salt; the emplacement of salt on mantle during extension, rather than during the later Pyrenean Orogeny, is indicated by the reworking of crustal and mantle clasts into Albian to Cenomanian conglomerates (Jammes et al., 2010). Ultimately, the salt layer developed considerable post-depositional relief, with diapirs located in both proximal and central (distal) portions of the extensional basin (Fig. 3b, c).

Syn-Stretching Salt Basins

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

Model

Syn-stretching salt is deposited in half-graben that developed during early rifting, so that the base salt has original topographic relief and the salt has variable thickness (Fig. 4a). The base-salt relief, the amount of thickness variation, and the presence or absence of salt on footwall highs all depend on when in the stretching history salt is deposited, the extension magnitude and rate, and the nature and duration of basin isolation. In addition, the total amount of extension experienced by the salt is a function of exactly when in the rifting history evaporite deposition begins.

image

Figure 4. Model of syn-stretching salt basin using template modified from Péron-Pinvidic & Manatschal (2009): (a) early stretching stage with salt deposition controlled by active faults; (b) late stretching stage with salt diapirism triggered by ongoing thick-skinned extension; (c) thinning stage with continued diapirism; (d) exhumation stage with only minor continued salt-related deformation; and (e) spreading stage showing salt concentrated in proximal areas.

Download figure to PowerPoint

As in the case of prerift evaporites, salt movement and diapirism are initiated by thick-skinned extension during the stretching stage. The primary differences are that mobility begins as soon as the salt is deposited and that evaporites continue to be deposited during ongoing extension. As long as salt is being deposited, flow is lateral and downward from above basement highs into growing half-graben and the top of the evaporite level remains roughly horizontal (Figs 4a and 5a, b). Once nonevaporite strata cover the salt after basin isolation ends, however, the overburden is also stretched, leading to reactive diapirism. Because the cover is thin, it separates almost immediately, so that salt breaks through to the surface and forms passive diapirs after only minimal further extension (Fig. 5c). During the remainder of the stretching stage, diapirs continue to grow vertically and widen as the intervening minibasins sink into the underlying salt (Figs 4b and 5d).

image

Figure 5. Schematic evolution of syn-stretching salt: (a) salt deposited in active rift basins; (b) salt continues to be deposited during ongoing extension, with salt flowing from footwalls to hangingwalls (arrows); (c) salt deposition ceases and overburden is deposited during ongoing extension, so that reactive diapirs are triggered immediately; (d) passive diapirism continues even after extension ends as long as there is a supply of deep salt.

Download figure to PowerPoint

According to the Péron-Pinvidic & Manatschal (2009) model, the thinning stage is marked by a shift in the locus of extension from proximal to distal areas. In this case, extension mostly ceases in the salt basin and now occurs primarily where there is little or no salt (Fig. 4c, d). Diapirs continue to grow until the deep salt layer is locally depleted, at which time they get buried, and little or no salt movement (depending on the original salt thickness) occurs during later extensional stages (Fig. 4d, e). Salt ends up principally in proximal parts of the margin and is mostly absent in distal areas (Fig. 4e). In contrast, if the early stretching faults are more widespread than depicted in the model, so that thinning occurs where salt was deposited, the evolution is more similar to that shown for prerift salt (Fig. 2c, e).

Examples

The classic examples of syn-stretching salt are provided by the conjugate margins of Iberia and Newfoundland (Fig. 6a). These margins form the type locality for the Péron-Pinvidic & Manatschal (2009) model, who described a long-lived extensional history: Upper Triassic to Middle Jurassic stretching; Middle Jurassic to Berriasian thinning; Valanginian to Aptian exhumation; and the onset of spreading during the Albian. Evaporites were deposited during the Late Triassic to Early Jurassic (Hubbard, 1988; Rasmussen et al., 1998), during the stretching stage. Although the ages of extension and evaporite deposition are broadly equivalent to those on the northern Iberian margin (defined here as prerift salt; Fig. 3), the two areas are quite different. On the northern Iberian margin, the salt and Rhaetian to Jurassic overburden represent an interlude without extension and thus had regional distribution prior to rifting, whereas on the western Iberian margin, salt was deposited only locally during ongoing rifting and there was no prekinematic overburden.

image

Figure 6. Iberia-Newfoundland conjugate margins, examples of syn-stretching salt: (a) map of southern North Atlantic showing location of lines and smaller map; (b) time section from Peniche Basin, offshore Portugal, showing thin salt and diapirs in relatively proximal half-grabens (modified from Alves et al., 2006); (c) time section from Whale and Horseshoe basins, offshore Newfoundland, illustrating relationship of salt diapirs to proximal rift-basin geometry [location shown in (e); modified from Balkwill & Legall, 1989]; (d) regional time section from offshore Portugal showing lack of salt in distal margin (modified from Alves et al., 2006; Sutra & Manatschal, 2012); (e) map of Newfoundland margin showing linear salt walls (pink) typically associated with underlying rift faults at the margins of basement highs (brown) (modified from Balkwill & Legall, 1989), with location of cross-section (c) indicated.

Download figure to PowerPoint

On the conjugate margins of Iberia and Newfoundland, salt was deposited in proximal extensional troughs, such as the Lusitanian and Peniche basins on the Iberian margin and the Whale, Horseshoe, and Jeanne d'Arc basins on the Newfoundland margin (e.g. Balkwill & Legall, 1989; Tankard et al., 1989; Rasmussen et al., 1998; Alves et al., 2002, 2006), but has not been recognized or reported from the most distal portions of either margin (Fig. 6b). Although the original spatial distribution of salt was controlled by the existing rift-basin architecture at the onset of deposition, the initial thickness distribution is unknown due to syn- and post-depositional movement on underlying faults (see Fig. 5a–c).

Salt diapirism was triggered by ongoing thick-skinned extension after the salt was buried by nonevaporite strata. Some pillows and diapirs are associated with the major normal faults (Fig. 6c, d) (Balkwill & Legall, 1989; Alves et al., 2002, 2006), but others have no spatial relationship with underlying faults due to complete decoupling by the salt (Jackson & Vendeville, 1994). Salt structures are typically linear, with salt walls up to 150-km long, 5-km wide and 4-km tall in the Whale Basin (Balkwill & Legall, 1989). Intervening minibasins have variable growth geometries due to the complex interaction of extensional and diapiric deformation. Diapirism continued, even after extension ceased, until the deep salt source was depleted. Thin-skinned, gravity-driven deformation was minimal due to the limited and discontinuous distribution of the salt.

Syn-Thinning Salt Basins

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

Model

Syn-thinning salt is deposited during the thinning or hyperextension stages, i.e., during development of the major extensional faults that thin the continental crust down to 10 km in thickness or less. Here, the focus is on the thinning stage, such that the salt basin forms over or near the major keystone fault block, or H-block (Fig. 1b), bounded by inwardly dipping conjugate faults, with salt thin or absent in more proximal areas where extension during the early stretching stage was concentrated (Fig. 7a). The early spatial and thickness distribution depends on the interplay between rift-basin architecture (including the amount of overlap between the stretching and thinning domains), the amount and distribution of nonevaporite synrift fill, and the timing and duration of evaporite deposition.

image

Figure 7. Model of syn-thinning salt basin using template modified from Péron-Pinvidic & Manatschal (2009): (a) early thinning stage with salt deposition controlled by active faults in area of H-block; (b) continued salt deposition during late thinning stage with increased offset of base salt on major thinning faults; (c) exhumation stage with salt tectonically emplaced and attenuated over serpentinized mantle, decoupled thin-skinned extension, and nappe emplacement; (d) spreading stage with continued thin-skinned deformation, diapirism, and allochthonous salt emplacement.

Download figure to PowerPoint

As in the case of syn-stretching salt, relief on the base salt increases during evaporite deposition (Fig. 7b) and early salt flow is from above fault footwalls into growing half-grabens (Fig. 5). Continued thinning after salt deposition leads to drape folding of the overburden and reactive diapirism (Fig. 7c), again with the degree of coupling depending on such factors as the salt thickness and the fault-displacement magnitude. Because thinning faults may have 5 km or more of throw, there is a greater tendency for coupling, with the salt highly attenuated or completely offset on the major faults. Attenuation of salt also occurs during mantle exhumation as the salt is stretched and thinned over the widening zone of exhumation (Fig. 7c). If there is enough salt remaining after exhumation, it may ultimately be extended over newly created oceanic crust (Fig. 7d).

Although there is certainly a thick-skinned component of salt deformation, gravity-driven thin-skinned deformation becomes increasingly important during the late thinning and hyperextension/exhumation stages due to a combination of overall basinward tilt of the extending salt layer and differential sedimentary loading. Thin-skinned, gravity-driven proximal extension is detached on a combination of the low-angle thinning faults and the salt, and is accommodated in distal areas by shortening and the development of an allochthonous salt nappe (Fig. 7c). The ramp-flat geometry of the base salt creates landward-shifting ramp basins (Rowan et al., 2004; Jackson & Hudec, 2005) in the overburden above fault hangingwalls. The combination of the original distribution of the salt and the bulk movement of salt basinward due to gravitational failure results in an eventual concentration of salt in distal portions of the margin (Fig. 7d).

Example

I propose here that the northern Red Sea (Fig. 8) is an example of syn-thinning salt. Rifting in the Red Sea initiated at about 30–27 Ma (Hughes et al., 1992; Bosworth et al., 2005) and oceanic spreading began at 5 Ma in the Southern Red Sea (Roeser, 1975). No further distinction of extensional phases (e.g., stretching vs. thinning) has been proposed, although there was a significant increase in basinal subsidence and proximal uplift at circa 20 Ma (e.g. Richardson & Arthur, 1988; Bohannon et al., 1989; Bosworth et al., 2005). An abandonment of proximal faulting and basinward shift in the locus of extension at the same time (Bosworth, 1994; Tubbs et al., 2013) suggests that the thinning stage may have commenced at 20 Ma. Evaporite deposition began at 14 Ma and ended at 5 Ma, immediately prior to the onset of spreading in the Southern Red Sea, although the upper part of the sequence in proximal areas is dominated more by siliciclastics than by evaporites (e.g., Heaton et al., 1995; Hughes & Johnson, 2005).

image

Figure 8. Map of the Red Sea and surrounding areas reconstructed to 10 Ma, during evaporite deposition, with thick black arrows showing opening direction (modified from Bosworth et al., 2005). The red box shows the approximate location of the seismic profiles illustrated in Figs 9 and 10.

Download figure to PowerPoint

There is considerable debate as to the nature and distribution of crust in the Red Sea due in large part to poor imaging beneath the thick, shallow evaporites. Although some have suggested that oceanic crust is widespread throughout the Red Sea (e.g., Le Pichon & Francheteau, 1978), most have interpreted oceanic crust to be confined to the axial trough of the Southern Red Sea (e.g., Cochran, 1983; Bosworth et al., 2005). Thin crust either landward of oceanic crust in the south or in the axial zone of the Northern Red Sea is variously interpreted to comprise rotated fault blocks (e.g. Cochran & Karner, 2007), exhumed mantle (e.g. Voggenreiter et al., 1988), or volcanic crust including SDRs (Mohriak et al., 2010). Given this uncertainty, I rely on geometries observed in new 3-D, depth-migrated seismic data to suggest that salt in the Northern Red Sea is syn-thinning. Given that salt deposition was synchronous throughout the Red Sea and that extension has progressed farther in the Southern Red Sea, what is syn-thinning salt to the north may be equivalent to syn-exhumation salt to the south. In any case, evaporite deposition predated any oceanic crust.

A dip-oriented seismic profile from the Arabian side of the Northern Red Sea (Fig. 9) shows that, although the top salt is relatively level, the base salt progressively steps down to the SW, with the largest step approximately 5 km in amplitude. The steps are associated with underlying low-angle faults and tilted fault blocks. The faults sole into a bright reflection that is interpreted as a mid-crustal shear zone that merges basinward with a rising Moho. The faults are interpreted as thinning faults because more proximal stretching faults and growth strata are truncated beneath a regional lower Miocene unconformity (e.g., onshore Midyan area; Tubbs et al., 2013). The relationships suggest that evaporite deposition postdated proximal stretching but was synchronous with distal thinning or hyperextension, although the salt may also have filled in some amount of relict fault-related topographic relief.

image

Figure 9. Uninterpreted (a) and interpreted (b) versions of 3-D depth-migrated seismic profile from the Saudi Arabian half of the northern Red Sea. The base salt is offset by thinning faults that detach in a mid-crustal shear zone that converges basinward with the Moho. Black lines within salt show recumbent isoclinal fold that reflects simple-shear deformation as upper part of sequence moved basinward relative to the portion of the evaporite sequence below the top of the ramp in the base salt (black arrow). No vertical exaggeration; data courtesy of Saudi Aramco.

Download figure to PowerPoint

Salt deformation was dominated by thin-skinned gravitational failure, with proximal extension and distal contraction (Heaton et al., 1995; Mougenot & Al-Shakhis, 1999; Bosworth et al., 2005; Tubbs et al., 2013). The evaporite décollement generally dips basinward from surface exposures onshore to at least 7-km depth offshore. Proximal areas are dominated by basinward-dipping growth faults and occasional diapirs, both active primarily during the late Miocene (siliciclastic-dominated portion of the general evaporite sequence) and rooted in the mostly welded salt level. Distal areas are characterized by inflated salt with internal simple-shear structures (Fig. 9), contractional folds and, at least in the Central Red Sea, extrusion of allochthonous salt out over oceanic crust (Mitchell et al., 2010). Between the two provinces is a zone of unusual growth geometries that may be misinterpreted as salt-evacuation structures (Fig. 10). Instead, these structures represent a translational province of basinward transport over a ramp-flat, mostly welded salt décollement (see Gibbs, 1984; Rowan et al., 2004; Jackson & Hudec, 2005), with the ramps formed by offset of the base salt on thinning faults. The result is a series of landward-shifting depocenters (ramp basins) associated with each presalt hangingwall that record the amount and (given adequate age control) timing of basinward translation.

image

Figure 10. 3-D depth-migrated seismic profile from the Saudi Arabian half of the northern Red Sea. Red lines in overburden show tops of carbonate buildups. Vertical lines indicate depocenter axes: orange pattern shows a half-turtle adjacent to a diapir; yellow lines show two sets of landward-shifting depocenters (ramp basins) in the same stratigraphy that record basinward translation over ramps in the salt décollement formed by the two major basement faults. Vertical exaggeration 2 : 1; data courtesy of Saudi Aramco.

Download figure to PowerPoint

Syn-Exhumation Salt Basins

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

Model

Syn-exhumation salt basins are unusually broad, with evaporites distributed over both the proximal and distal portions of the margin. The salt is deposited after the bulk of brittle upper-crust extension (thinning and hyperextension phases) has ceased but before final breakup and accretion of normal oceanic crust. In the Péron-Pinvidic & Manatschal (2009) model, this is during or after exhumation and serpentinization of subcontinental mantle, but it could also be during or after the emplacement of SDR sequences (see Discussion section below). In either case, because crustal faulting has largely ceased, the base salt has little relief over most of its length (Fig. 11a). The exception is in the most distal area, where some detachment faults that exhume the mantle, in addition to any fault blocks within the ocean–continent transition zone, offset any presalt stratigraphy and the base salt. The detachment faults will not be exposed at the sea floor (Jammes et al., 2010); instead, depending on the duration of mantle exhumation and the timing of evaporite deposition, the salt will be tectonically stretched as the zone of exhumation widens (Fig. 11b; see also Hudec et al., 2013).

image

Figure 11. Model of syn-exhumation salt basin using template modified from Péron-Pinvidic & Manatschal (2009): (a) early exhumation stage with deposition of sag basin (orange) and salt after almost all crustal faulting has ceased, so that there is little offset of the base salt; (b) late exhumation stage with separation of synrift and sag sequences and salt attenuation over newly exhumed mantle; (c) spreading stage and development of thin-skinned deformation due to gravitational failure of margin. Note that although serpentinized mantle is shown, it is also possible that distal salt is deposited over volcanic crust.

Download figure to PowerPoint

Because of the lack of any significant presalt faulting in all but the most distal area, thick-skinned extension is not a factor in the subsequent salt evolution. Instead, salt mobility is triggered by gravity gliding as the margin tilts basinward due to differential thermal subsidence (e.g. Brun & Fort, 2011) and/or stretching of the salt during ongoing crustal extension beneath the salt (Hudec et al., 2013), with gravity spreading due to sediment progradation later becoming dominant in some areas (Rowan et al., 2012a). Deformation initiates soon or immediately after evaporite deposition ceases and possibly even during ongoing deposition (so-called salt drainage; Quirk et al., 2012; Davison et al., 2012). The margin is characterized by a proximal thin-skinned extensional domain, an intermediate translational domain dominated by salt evacuation and diapirism, and a distal contractional domain with salt-cored detachment folds and associated thrusts and squeezed diapirs (e.g. Fort et al., 2004; Fig. 11c). There is a bulk movement of salt basinward, marked by updip thinning and attenuation and downdip inflation and internal shortening (see Cartwright et al., 2012). Allochthonous salt is common, including a frontal nappe where salt advances over oceanic crust and aggrading sediment. Although the conjugate margins in Fig. 11 are roughly symmetric, they may be highly asymmetric, depending on exactly where mantle exhumation and ultimate breakup occur, so that salt may be unevenly distributed between the opposite sides of the ocean basin.

Examples

I characterize the largest and to date most hydrocarbon-prolific passive-margin salt basins, including conjugate basins in the South Atlantic and Gulf of Mexico, as syn-exhumation salt. The traditional view is that single evaporite depocenters were subsequently divided by the accretion of oceanic crust (e.g. Evans, 1978; Duval et al., 1992; Davison, 1999; Karner & Gamboa, 2007; Pindell & Kennan, 2007; Mohriak et al., 2008). Others have argued that salt in some of these conjugate basins (such as the Kwanza and Campos basins) was never contiguous but separated by proto-spreading centres (e.g. Jackson et al., 2000; Quirk et al., 2013). Imbert & Philippe (2005) suggested that the Gulf of Mexico originally comprised one salt basin that was deposited over actively forming oceanic or proto-oceanic crust (characterized by SDRs) with no exposed spreading centre until ultimately splitting into two salt basins. I have defined syn-exhumation salt as predating final breakup, described as the localization of complete plate separation in a thermally and magmatically weakened spreading system of normal oceanic crust (Lavier & Manatschal, 2006; Péron-Pinvidic & Manatschal, 2009) or rupture immediately followed by seafloor spreading (Huismans & Beaumont, 2011). Whether the salt overlies thinned continental crust, exhumed mantle, volcanic crust with SDRs, or some combination is immaterial to the classification of the salt as syn-exhumation and pre-breakup.

Gulf of Mexico

There is broad consensus on the origin and timing of the Gulf of Mexico, with rift initiation in the Late Triassic and the onset of oceanic spreading by the latest Callovian to early Oxfordian as the Yucatan block moved away from North America, first to the SE and then rotating counter-clockwise about a pole located near western Cuba (e.g. Salvador, 1991; Pindell & Kennan, 2001, 2009; Kneller & Johnson, 2011). Evaporites formed at the end of this extensional history, primarily during the Callovian (Salvador, 1987). Hudec et al. (2013) suggested that spreading did not commence until the Kimmeridgian to Tithonian, so that there was a phase of crustal stretching between the end of salt deposition and the beginning of oceanic crust formation. In any case, the nature of transitional crust underlying depositional salt between the shoreline and abyssal plain is controversial due to deep burial and shallow salt. Recent publications include those that invoke: thinned continental crust (Roberts et al., 2005); proximal rifted continental crust and distal proto-oceanic crust (Pindell & Kennan, 2007); oceanic and proto-oceanic crust (Imbert & Philippe, 2005; Mickus et al., 2009); ultraslow-spreading lithosphere interpreted to comprise serpentinized mantle and/or areas of thin oceanic crust (Kneller & Johnson, 2011); and, for the northern Gulf of Mexico, hyperextended continental crust with a lateral transition from exhumed mantle in the west and centre to proto-oceanic crust in the east (Rowan et al., 2012b).

Despite this uncertainty, several lines of evidence show that the salt is syn-exhumation. First, the original extent of the evaporites is enormous, spanning the proximal onshore to the distal deepwater (Fig. 12). Second, deposition occurred just prior to final breakup and seafloor spreading. Third, the salt forms the upper portion of a thick sag basin in the southern Gulf of Mexico (Miranda et al., 2013). Finally, and in keeping with the previous point, the base salt is mostly unfaulted, whether it overlies SDRs (Fig. 13) or hyperextended crust and exhumed mantle (Fig. 14). In other words, salt was deposited after the bulk of brittle upper-crustal extension had ceased. A prominent exception is the so-called ‘stepup fault’ or ‘inner ramp’ (Hudec & Peel, 2010; Barker & Mukherjee, 2011; Pindell & Horn, 2012), but this marks the breakup edge of autochthonous salt, with more distal salt representing early allochthonous advance over oceanic crust (Fig. 14). In their most recent interpretation, Hudec et al. (2013) suggest that the inner ramp is not the limit of depositional salt sensu strictu but simply the boundary between oceanic crust and a zone of parautochthonous salt that was stretched over extended transitional crust after evaporite deposition (Fig. 12).

image

Figure 12. Map of Gulf of Mexico with present-day distribution of salt (modified from Hudec et al., 2013). Approximate locations of seismic profiles indicated by dashed ellipses.

Download figure to PowerPoint

image

Figure 13. Uninterpreted (a) and interpreted (b) versions of prestack depth-migrated 2-D seismic profile from the northeastern Gulf of Mexico. The thin salt is above a combination of more proximal rotated fault blocks of continental crust and more distal volcanic crust, with only minor offset of the base salt on several faults. A boundary between more and less reflectivity (deeper and shallower, respectively) is interpreted to represent the brittle-ductile transition between the upper and lower continental crust. Thin and thick purple lines are interpreted volcanic flows seaward-dipping reflectors (SDRs) and saucer-shaped intrusive sills, respectively. Vertical exaggeration 2 : 1, approximate location shown in Fig. 12. Data from SuperCache survey, courtesy of Dynamic Data Services.

Download figure to PowerPoint

image

Figure 14. Uninterpreted (a) and interpreted (b) versions of prestack depth-migrated 2-D seismic profile from the northwestern Gulf of Mexico. In (a), the red and black arrows highlight key basinward- and landward-dipping reflectors interpreted as a low-angle detachment fault and the Moho, respectively. In (b), the deep (autochthonous) salt level is above a combination of hyperextended continental crust, interpreted exhumed mantle and a possible thin sag sequence, with offset of the base salt on only one fault. The base salt ramps up basinward over the stepup fault and extends over oceanic crust as an allochthonous nappe, and a large, partly welded canopy is present at shallow levels. Rotated presalt fault blocks are visible above the low-angle crustal detachment fault (red) that can be mapped over an area of 200 × 100 km and that merges downward with a rising Moho. Vertical exaggeration 2 : 1, approximate location shown in Fig. 12. Data from SuperCache survey, courtesy of Dynamic Data Services.

Download figure to PowerPoint

Postsalt deformation in the northern Gulf of Mexico began immediately after salt deposition due to gravity gliding caused by basinward tilt of the margin as newly formed oceanic crust subsided (e.g. Peel et al., 1995; Rowan et al., 2004; Fort & Brun, 2012) or due to stretching of the salt and its cover during ongoing crustal extension (Hudec et al., 2013). Upper Jurassic to Lower Cretaceous extension was located near the proximal edge of the salt basin and was accommodated by shortening and nappe emplacement at the distal toe (see Fig. 14; Imbert & Philippe, 2005; Pindell & Kennan, 2007), a distance of up to greater than 500 km. This basinward translation set up Mesozoic depocenters and intervening areas of inflated salt that evolved into diapirs. Extension, translation, and contraction continued during the Cenozoic but during this time was driven more by progradational loading and consequent gravity spreading (e.g. Worrall & Snelson, 1989; Peel et al., 1995; Rowan et al., 2004, 2012a), although some gravity gliding was caused by proximal uplift of the margin (Jackson et al., 2011; Dooley et al., 2013). Allochthonous salt is almost ubiquitous, ranging from individual sheets less than 100 km2 in size to enormous, sometimes multi-tiered canopies covering more than 80 000 km2 (e.g. Diegel et al., 1995; Pilcher et al., 2011). Cenozoic gravitational failure was partitioned in spatially and temporally complex patterns between the autochthonous and allochthonous levels, depending on large part on the size, position, and base-salt relief of the canopies (Rowan & Inman, 2006; Rowan et al., 2009).

South Atlantic

The central South Atlantic (Fig. 15) contains salt basins on both the western, Brazilian margin (Santos, Campos, Espirito Santo, Cumuruxatiba, Jequitinhonha, Camamu, Sergipe-Alagoas) and eastern, African margin (Namibe, Benguela, Kwanza, Lower Congo, South Gabon, Rio Muni). Somewhat surprisingly, there is even less consensus on the crustal architecture and timing than in the Gulf of Mexico. Estimates of the beginning of rifting range from the Berriasian (e.g. Karner et al., 2003; Mohriak et al., 2008; Lentini et al., 2010; Unternehr et al., 2010) to the late Valanginian (Quirk et al., 2013) to as late as the early Barremian (Meisling et al., 2001), and final breakup is thought to have occurred either during the Barremian (Jackson et al., 2000; Marton et al., 2000; Quirk et al., 2013) or near the Aptian-Albian boundary (Meisling et al., 2001; Karner et al., 2003; Karner & Gamboa, 2007; Torsvik et al., 2009; Unternehr et al., 2010; Blaich et al., 2011; Mohriak & LeRoy, 2013).

image

Figure 15. Present-day Aptian salt thickness in the South Atlantic shown on a map reconstruction immediately prior to oceanic breakup (modified from Lentini et al., 2010); original salt distribution would have been broadly similar, although there has been bulk movement of salt basinward. ‘COB’ indicates interpreted continental-oceanic boundary; salt basins in italics. Dashed ellipses indicate the approximate locations of the profiles shown in Figs 16 and 17.

Download figure to PowerPoint

The underlying cause for the discrepancy in breakup age centres on the origin of the so-called sag basins (or presalt wedges). These are broad, mostly unfaulted packages of Barremian to Aptian strata up to 7 km thick (e.g. Henry et al., 1995, 2004; Karner & Gamboa, 2007) between salt and a deeper unconformity that overlies rifted crust. In older interpretations, the sag basin and salt thin both landward and basinward, but newer data suggest that the distal limit is more abrupt where the basin steps up onto an outer high of either oceanic or continental affinity (Lentini et al., 2010; Unternehr et al., 2010; Zalan et al., 2011; Davison et al., 2012; Quirk et al., 2013). Some consider the sag basin and evaporites to represent the earliest postrift strata, deposited above the breakup unconformity and thus after plate separation (e.g. Jackson et al., 2000; Marton et al., 2000; Quirk et al., 2013), whereas others interpret the sag and salt as part of the synrift section that predates breakup (e.g. Karner et al., 2003; Karner & Gamboa, 2007; Mohriak et al., 2008; Unternehr et al., 2010; Blaich et al., 2011).

The evaporites themselves have variable age estimates ranging from as early as 124 Ma to as late as 110 Ma (Davison, 2007; Karner & Gamboa, 2007; Mohriak & LeRoy, 2013; Quirk et al., 2013), so were either pre- or post-breakup depending on the interpretation. Thus, the salt was deposited either in a single depocenter that was subsequently separated into the Brazilian and African basins (e.g. Karner & Gamboa, 2007; Mohriak et al., 2008; Torsvik et al., 2009; Lentini et al., 2010) or in separate basins on either side of a subaerial spreading centre (e.g., Jackson et al., 2000; Marton et al., 2000; Davison et al., 2012; Quirk et al., 2013). Furthermore, there is disagreement on what type of crust underlies the most distal autochthonous salt: thin continental crust, with or without a significant proportion of magmatic rocks (e.g. Mohriak et al., 2008; Lentini et al., 2010; Mohriak & LeRoy, 2013); volcanic crust, whether oceanic or consisting of SDRs (e.g., Jackson et al., 2000; Marton et al., 2000; Torsvik et al., 2009; Quirk et al., 2013); exhumed subcontinental mantle (e.g. Unternehr et al., 2010; Zalan et al., 2011); or exhumed lower continental crust (Sibuet & Tucholke, 2013).

Taking into consideration all the various models cited above, the newest seismic data with the best deep images, and analogies to other passive margins such as the northern Gulf of Mexico, I find interpretations similar to those by Unternehr et al. (2010) and Zalan et al. (2011) to be the most compelling. What is beyond question is that evaporite deposition postdated the bulk of crustal thinning, so that there is generally only local and minor offset of the base salt (Fig. 16). There are certainly some large faults, especially on the Brazilian margin, but much of the base-salt relief is due to some combination of differential compaction and drape above older faults, reactivation due to loading by the excess salt, and post-breakup tectonics (Davison, 2007; Mohriak et al., 2008; Davison et al., 2012). One prominent exception is the step up of the base salt onto either oceanic crust (Fig. 16a) or exhumed mantle (Fig. 16b). In any case, the salt was most likely deposited in a single basin that was subsequently separated during final breakup and accretion of normal oceanic crust. The salt and presalt sag basin are underlain by hyperextended continental crust and, more distally, some combination of exhumed mantle (as depicted in Fig. 16) and SDRs.

image

Figure 16. Cross-sections from interpreted seismic data in the South Atlantic: (a) profile from the Lower Congo Basin, Angola (modified from Unternehr et al., 2010); (b) profile from the Campos Basin, Brazil (modified from Zalan et al., 2011). Both show salt with relatively low-relief bases over sag basins and hyperextended continental crust, salt concentrated in distal areas, allochthonous salt ramping up over stepup faults and emplaced over oceanic crust (a) or mantle (b), and exhumed subcontinental mantle that is infiltrated and/or serpentinized (diagonal lines). Vertical exaggeration 2 : 1.

Download figure to PowerPoint

Gravitational failure may have begun while salt was still being deposited (Davison et al., 2012; Quirk et al., 2012) but was certainly ongoing during and after deposition of the overlying Albian carbonates. Basinward movement was in some cases convergent or divergent (Cobbold & Szatmari, 1991). Proximal extension is recorded by a combination of basinward-dipping and counterregional faults, including the well known Cabo Frio Fault or so-called Albian gap in the Santos Basin, often separating the oldest suprasalt section into extensional rafts (e.g. Duval et al., 1992; Demercian et al., 1993; Mohriak et al., 1995; Marton et al., 2000; Fort et al., 2004). Translation over ramps in the base salt, for example where the salt drapes over the Atlantic Hinge Zone in offshore Angola, created a series of landward-shifting depocenters (Hudec & Jackson, 2004; Rowan et al., 2004; Jackson & Hudec, 2005). Distal contraction is characterized by folds, thrusted folds, squeezed diapirs, squeezed and inflated salt massifs, and thrust emplacement of allochthonous salt out over oceanic crust (e.g. Demercian et al., 1993; Cobbold et al., 1995; Marton et al., 2000; Rowan et al., 2004; Hudec & Jackson, 2004; Brun & Fort, 2004; Fiduk & Rowan, 2012). Allochthonous salt is present, but not to the same extent as in the Gulf of Mexico. Moreover, the canopies that do exist did not serve as secondary décollements for gravitational failure as they did in the Northern Gulf of Mexico.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

The classification of passive-margin salt basins proposed in this paper is based on the model of Péron-Pinvidic & Manatschal (2009). Again, there are other published models with minor to major divergence from this one (e.g. Whitmarsh et al., 2001; Lavier & Manatschal, 2006; Reston, 2009; Huismans & Beaumont, 2011; Pérez-Gussinyé, 2013). The details of real crustal architecture and evolution will, of course, vary from this and other models and will vary between different margins with similar histories. Consequently, the original distribution of salt and the styles of salt-related deformation will also be highly variable.

Moreover, the model presented here is simplified. Complications and combinations can take several forms. First, passive-margin evolution is progressive and one style of extension is likely to overlap in space and time with another style. Second, evaporite deposition may span the transition between two consecutive stages. For example, salt might be deposited during the late thinning stage and on into the mantle-exhumation stage. Third, passive-margin development may get younger along strike as continents ‘unzipper’. Thus, evaporite deposition might occur while one area is undergoing thinning but a more mature segment is already in the exhumation stage, as suggested here for the Red Sea. Finally, a given margin may have more than one period of salt deposition. For example, both the Sergipe-Alagoas Basin (Karner & Gamboa, 2007) and the Atlantic margin of the United States (Post et al., 2013) have proximal, older salt in graben settings and distal, younger salt overlying SDRs.

Despite these caveats, the classification of passive-margin salt basins into prerift, stretching, syn-thinning, and syn-exhumation is more appropriate than the traditional division into prerift, synrift, and postrift salt. It better explains various aspects of salt basins ranging from the areal distribution of salt to the styles and timing of suprasalt deformation. Table 1 lists some of these features; although any one characteristic may occur in different settings, each type of salt basin has a unique mixture that can be used to distinguish them.

Table 1. Characteristic features of different categories of passive-margin salt basins
 PreriftSyn-stretchingSyn-thinningSyn-exhumation
Depositional extentGenerally widespread – depends on prior historyTypically proximal and often localizedMostly distalWidespread
Original thickness variationsTypically minor – depends on prior historySignificant – deposited in half-grabensSignificant – deposited in half-grabensMinor
Present distributionWidespread but more common in proximalMostly if not entirely proximalMostly distalMostly distal
Original base-salt geometryGenerally low-relief – depends on prior historyHigh-reliefHigh-reliefMostly low-relief
Present base-salt geometryHigh-reliefHigh-reliefHigh-reliefMostly low-relief
Prekinematic coverYesNoNoNo
TriggerThick-skinned extensionThick-skinned extensionThick-skinned extension and gravity gliding Gravity gliding
Dominant deformation styleThick-skinnedThick-skinnedThin-skinnedThin-skinned
Extensional structuresUbiquitousUbiquitousProximalProximal
Contractional structuresRareNoDistalDistal
Diapir locationsCommonly related to underlying faultsCommonly related to underlying faultsRarely related to underlying faultsNo relationship to underlying faults
Allochthonous saltRareRareCommonAbundant

Syn-exhumation salt basins include the four largest and, to date, most hydrocarbon-rich passive-margin salt provinces in the world: the northern and southern Gulf of Mexico, the Santos to Espirito Santo basins of Brazil, and the Kwanza to South Gabon basins of Africa. In the following sections, I examine several puzzling or uncertain aspects of these syn-exhumation salt basins that merit further discussion.

Magmatic influence

As summarized above for both the South Atlantic and the northern Gulf of Mexico, the nature of crust beneath the most distal autochthonous salt is enigmatic. Are these margin segments magma-poor, dominated in the distal domain by exhumed mantle, or magma-rich, with widespread development of SDRs? Certainly, there are SDRs visible either just along strike from salt, such as in the Pelotas and Jacuipe basins to the south and north, respectively, of the major Brazilian salt basins (e.g. Mohriak et al., 1998; Jackson et al., 2000; Blaich et al., 2011), or beneath thin salt such as in the northeastern Gulf of Mexico (Fig. 13) (Imbert, 2005; Post, 2005; Pindell & Kennan, 2007). But do the SDRs extend beneath the thicker salt where there is generally poor imaging, such that the major salt basins are magma-rich?

Modern data and interpretations suggest just the opposite, that the largest salt basins occur in relatively magma-poor settings (e.g. Unternehr et al., 2010; Kneller & Johnson, 2011; Zalan et al., 2011; Rowan et al., 2012b). In the north-central and northwestern Gulf of Mexico, for example, new long-offset data show the Moho beneath oceanic crust climbing landward to a level just beneath the autochthonous salt (Fig. 17; see also Fig. 14). Moreover, the Moho reflector changes polarity in Fig. 17: it shows a positive acoustic impedance contrast between oceanic crust and asthenospheric mantle where the Moho is subhorizontal in the oceanic domain; where it is dipping basinward, however, it shows a negative acoustic impedance contrast, interpreted here as the boundary between oceanic crust and serpentinized subcontinental mantle. The areas where exhumed mantle is interpreted (Figs 14 and 17) are in the centre of the basin, where the Louann salt was originally thick (see Fig. 12). Farther to the east, where the Louann was originally thin, there are clear SDRs just beneath the salt (Fig. 13).

image

Figure 17. Uninterpreted (a) and interpreted (b) versions of prestack depth-migrated 2-D seismic profile from the north-central Gulf of Mexico. In (a), the black arrows highlight a reflector beneath the stepup fault that dips basinward between the autochthonous salt level and the oceanic Moho level; note that it has opposite polarity to the oceanic Moho at bottom right. In (b), the dipping event is also interpreted as the Moho, with the polarity reversal possibly representing the changing acoustic impedance contrast between normal oceanic crust and asthenospheric mantle (basinward) or serpentinized, exhumed subcontinental mantle (landward), such that exhumed mantle is present just beneath the salt and a thin sag sequence. Vertical exaggeration 2 : 1, approximate location shown in Fig. 12. Data from SuperCache survey, courtesy of Dynamic Data Services.

Download figure to PowerPoint

In the South Atlantic, Blaich et al. (2011) showed that the SDRs of the Pelotas and Walvis basins die out to the north, into the Santos/Campos and Benguela/Kwanza basins, respectively. Moreover, the prominent coastal magnetic anomalies associated with the SDRs lose magnitude and gradually disappear in the same areas. Seismic data from the transition between the Santos and Pelotas basins show that the presalt sag sequence, the salt itself, and early postsalt strata all thin laterally and onlap the top of the Pelotas Basin SDR package (Fig. 18). A similar scenario appears to exist in the Central Atlantic, where SDRs and coastal magnetic anomalies fade and vanish going north into the Scotian and Moroccan salt basins (Wu et al., 2006; Labails et al., 2010; Tari et al., 2012; Louden et al., 2013). In short, there appears to be a consistent pattern observed on the largest passive-margin salt basins, with the salt thickest where there is scant evidence for significant volumes of magmatic rocks and thinning onto margin segments with SDRs.

image

Figure 18. 2-D, time-migrated seismic profiles from the transition between the Santos and Pelotas basins, Brazil: (a) dip line from northern Pelotas Basin with prominent seaward-dipping reflector (SDR) package that is separated from oceanic crust by a stepup fault and is overlain by thin salt and a sag sequence that onlaps the top of the volcanic crust; (b) strike line between the northern Pelotas and southern Santos basins showing the transition from volcanic to rifted continental crust, with the sag sequence, salt and Albian all thinning and onlapping onto the paleo-topographic high formed by subaerial volcanics. Vertical white lines show tie points between the two profiles. Data courtesy of WesternGeco.

Download figure to PowerPoint

Uplift and subsidence

Magma-poor passive margins have somewhat enigmatic uplift and subsidence histories. Below, I summarize some of the observations and processes that may influence the spatial distribution and thickness of syn-exhumation salt. Uplift and subsidence on magma-rich margins are not considered.

Breakup unconformities and uplift

So-called breakup unconformities are traditionally viewed as marking final breakup and the onset of oceanic spreading, but they appear to correlate instead with late thinning and mantle exhumation. For example, a proximal unconformity on the Newfoundland margin cuts out the Tithonian to Barremian (Balkwill & Legall, 1989) and a similar feature on the proximal Iberian margin cuts out the Valanginian to mid-Aptian (Alves et al., 2002). However, mantle exhumation on these margins spanned the Valanginian to Aptian, making the unconformities syn-exhumation and pre-breakup (Péron-Pinvidic et al.,2007; Sibuet et al., 2007; Tucholke et al., 2007). A similar pattern is observed on the northern Iberian margin, where the unconformity ranges from late Aptian in the west to middle Albian in the east (Roca et al., 2011), when thinning and exhumation occurred (Jammes et al., 2010). There is no oceanic crust in the eastern Bay of Biscay or Pyrenees due to insufficient extension, yet the unconformity is prominent, demonstrating that it cannot be related to final breakup (Roca et al., 2011).

The examples in the previous paragraph are from prerift or syn-stretching salt basins, but similar relationships are observed in syn-exhumation salt basins. In the South Atlantic salt basins, an unconformity underlies the sag basins and is dated as Barremian to lower Aptian (e.g. Karner et al., 2003; Davison et al., 2012; Quirk et al., 2013). The geometries suggest that it marks the end of the thinning stage and is thus pre-breakup. In the northeastern Gulf of Mexico, there is a prominent unconformity above normal-thickness continental crust on the proximal Florida Platform, where salt is largely absent. In a more distal position, the correlative unconformity is about 1.5 km beneath the salt, similar to what is observed in the South Atlantic (M.G. Rowan, unpubl. results).

Several mechanisms have been proposed to explain regional uplift on magma-poor, hyperextended margins, although the location and breadth of uplift varies for each process. First, isostatic compensation of mass redistributed by necking and rupture has been invoked to explain proximal breakup unconformities (Braun & Beaumont, 1989). Second, cold subcontinental mantle displaced basinward during distal exhumation is replaced in more proximal positions by hot asthenospheric mantle (Karner & Gamboa, 2007; Unternehr et al., 2010). Third, extension of the lower crust, which should cause subsidence, must be accompanied by thinning of the lithospheric mantle, which leads to heat advection and uplift (Karner et al., 2003; Karner & Gamboa, 2007; Sutra & Manatschal, 2012). Fourth, extreme thinning in distal areas may be accompanied by mantle infiltration, with consequent heating and uplift (Péron-Pinvidic & Manatschal, 2009). Fifth, serpentinization of exhumed subcontinental mantle generates buoyancy (e.g. Péron-Pinvidic & Manatschal, 2009; Pérez-Gussinyé, 2013). Finally, channel flow of hot, viscous lower crust toward the rift axis may lead to distal uplift (Huismans & Beaumont, 2011). Whatever the mix of processes may be, those active in distal areas might explain the unconformities at the base of the sag sequence and those active in proximal areas might generate the classic breakup unconformities and provide updip limits to evaporite deposition.

Subsidence and sag basins

The unconformities are onlapped and covered by strata that are pre-breakup in age. In proximal parts of the Iberia-Newfoundland margins, the oldest post-unconformity strata are Aptian, yet spreading commenced in the Albian (Alves et al., 2002). In the Basque Pyrenees, the syn-exhumation upper Albian is conformable to underlying strata in more distal positions but unconformably overlies progressively older units toward the proximal rift shoulders (J. A. Muñoz & E. Roca, pers. comm., 2010). These examples document regional subsidence events that predated breakup and subsequent cooling and thermal subsidence of oceanic crust. More importantly here, distal unconformities are overlain by the syn-exhumation sag-basin fill, including the evaporites, in the South Atlantic and the Gulf of Mexico.

What processes might explain the subsidence responsible for the sag basins and evaporites in syn-exhumation salt basins? As many of the causes for uplift cited above involve heat, regional subsidence may represent subsequent cooling that is also enhanced by sedimentary loading. Assuming that evaporite deposition predates oceanic spreading, it is likely some combination of thinned and heated continental crust, infiltrated mantle and serpentinized subcontinental mantle that cools and subsides. On the Iberian margin, paleobathymetric data from wells show that mantle was exhumed to shallow water depths but then subsided rapidly (Péron-Pinvidic & Manatschal, 2009).

It is possible that syn-thinning to syn-exhumation uplift and subsidence are somewhat diachronous, with minor subsidence beginning in more proximal positions, as uplift continues more distally, and then progressing basinward. This is compatible with facies distribution in the upper part of the presalt sag sequence on the Angolan margin, where shallowing west of the Atlantic Hinge Zone was coeval with minor subsidence to the east (Karner et al., 2003), and with basinward shifting of depocenters in the sag sequence of the southern Gulf of Mexico (Miranda et al., 2013). Furthermore, variations in sag-basin thickness across the South Atlantic and along strike on both margins (Lentini et al., 2010) may record a response to complex spatial patterns of subcontinental-mantle flow toward areas of exhumation. As the evaporites form the upper part of the sag sequence, any pattern of basinward or lateral shifting of subsidence likely impacted the original salt thickness as well.

An intriguing aspect of the subsidence history in both the South Atlantic and the Gulf of Mexico is that both the top and base of the distal toe of depositional salt are deeper than the top of oceanic crust (Figs 18 and 19). The top salt was near sea level at the end of salt deposition, as shown by the presence of shallow-water carbonates (South Atlantic; Azevedo et al., 1987) or eolian sands (Gulf of Mexico; Salvador, 1987) immediately above the salt, yet is below normal oceanic crust that was presumably emplaced at water depths of about 2.6 km (e.g. Taylor et al., 1999). Thus, a major phase of subsidence, up to 3 km or more in distal areas, must have occurred after the end of salt deposition and before or during accretion of oceanic crust.

image

Figure 19. Uninterpreted (a) and interpreted (b) versions of prestack depth-migrated 2-D seismic profile from the northeastern Gulf of Mexico. A prominent ‘stepup’ fault that separates oceanic crust from seaward-dipping reflectors (SDRs) and possible hyperextended continental crust beneath (question marks) merges downward with the Moho at the hinge between the landward-dipping continental Moho and the subhorizontal oceanic Moho. Antithetic faults that offset the salt and growth strata in the overburden document at least some movement after salt deposition, probably during early emplacement of oceanic crust. Vertical exaggeration 2 : 1, approximate location shown in Fig. 12. Data from SuperCache survey, courtesy of Dynamic Data Services.

Download figure to PowerPoint

Two explanations have recently been put forth to explain this significant late subsidence event. First, Hudec et al. (2013) suggested that salt in the Gulf of Mexico was stretched and thinned above newly formed transitional crust prior to spreading, thereby dropping the top salt by over 3 km. Subsequent emplacement of oceanic crust at about 2.6 km separated the salt into the two conjugate margins and created the ‘inner ramps’ (equivalent to stepup faults), 1–4 km high steps that either bound the salt or mark the transition between stretched parautochthonous salt and allochthonous nappes that flowed out over oceanic crust and aggrading sediment. An important aspect of this model is that there is no crustal subsidence because only the top salt sinks. Yet both the presalt sag sequence in the southern Gulf of Mexico (Miranda et al., 2013) and observed SDR sequences in the northeastern Gulf of Mexico (Fig. 19) are also beneath the level of oceanic crust, and a similar geometry exists in the southern Santos Basin of Brazil (Fig. 18). Although the presalt sequence has not been penetrated in the distal portions of the Gulf of Mexico, lacustrine carbonates are well known just beneath the salt in the deepwater Santos Basin (e.g. Mann & Rigg, 2012; Quirk et al., 2013). Thus, there must have been a major subsidence event that affected not just the top of salt, but also the entire crust.

The second recent model that explains the relative levels of salt and oceanic crust invokes late tectonic subsidence. Pindell et al. (2013) suggest that the sag sequence and the salt form the hangingwall of a landward-dipping shear zone (the ‘outer marginal detachment’, equivalent to the inner ramp or stepup fault) that merges into the Moho at the base of the necking zone. Furthermore, it is the tilting of the hangingwall that creates the accommodation both for near sea-level deposition of sag-sequence strata and evaporites at magma-poor margins and for SDR development at magma-rich margins. Although the model places exhumed sub-continental mantle in the footwall in order to explain how salt can be deposited very close to global sea level while constantly subsiding in the hangingwall, both the examples in Pindell et al. (2013) and those here (Figs 17, 18 and 19) show evidence for normal oceanic crust in the immediate footwall rather than exhumed mantle. Even if mantle exhumed near sea level does indeed form the footwall, it must drop in order to end up at approximately the same depth as oceanic crust. Again, it is likely that there was a significant component of non-tectonic subsidence in addition to extension on the outer marginal detachment.

Layered evaporite sequences

Syn-exhumation salt basins are unusual in that they have remarkably pure evaporite sequences. Most salt basins have sometimes considerable proportions of non-evaporite interbeds such as carbonates, mudstones and coarser siliciclastics, and volcanics or shallow intrusives. Examples include broad intercontinental basins such as the Permian Zechstein and Upper Triassic Keuper of Europe, narrower rift basins such as the Neoproterozoic Adelaide rift of South Australia, and foreland basins such as the Upper Carboniferous Paradox Basin of the south-western United States (e.g. Brinkmann & Lögters, 1968; Hite & Buckner, 1981; Preiss, 2000; Warren, 2006). In contrast, the Callovian Louann Salt of the Gulf of Mexico is composed almost entirely of halite, with small amounts of dolomite, anhydrite, and potassium salts (Salvador, 1991), and the Aptian salt of the South Atlantic comprises mostly halite with minor anhydrite and other evaporites such as carnallite (e.g. Gamboa et al., 2008; Fiduk & Rowan, 2012). Moreover, the Aptian salts are poor in MgSO4, which is indicative of hydrothermal water–rock interaction with the most likely host being basalt (Jackson et al., 2000; Davison, 2007).

The almost complete lack of interbedded non-evaporite lithologies has two primary implications. First, topographic relief during salt deposition must have been very subdued, so that little siliciclastic material made it into all but the most proximal parts of the evaporite basin. This is supported by the distribution of sedimentary facies of both the presalt sag fill and the suprasalt Albian on the Brazilian margin (Quirk et al., 2013). Second, the evaporite basin effectively never had large influxes of fresh water, which suggests lack of major onshore drainage into the evaporite basin. It is also probable that the basins were effectively completely isolated. Sea water probably never or rarely spilled over the top of the barrier between the salt basin and world ocean during sea-level highstands (Karner et al., 2003); instead, it most likely percolated through the barrier (Davison et al., 2012).

General model for syn-exhumation salt basins

The various observations and similar patterns in different basins lead to a simplified, general model for syn-exhumation salt basins. It is based on two key elements. First, passive margins have hyperextended continental crust whether they are magma-poor or magma-rich (Figs 13 and 14; see also Péron-Pinvidic et al., 2012; Manatschal & Karner, 2012). Second, the processes of mantle and/or lower–crustal exhumation, sag-basin development and SDR emplacement are all broadly coeval, spanning the time between the end of thinning and the onset of spreading. Thus, the distal wedge of thinned continental crust may be underlain by, and grade distally into, serpentinized subcontinental mantle, with only minor magmatic influence (magma-poor margin; Fig. 20a), or it may be overlain by and grade into SDR sequences (magma-rich margin; Fig. 20b). Whether or not there is any serpentinized mantle beneath the SDRs is unknown, but it is liable to be less prevalent due to the greater burial of the subcontinental mantle beneath the volcanics. Moreover, the degree of serpentinization in salt basins is also unknown. Although salt that is being deposited and/or stretched during mantle exhumation may inhibit the downward percolation of sea water, reflux (or downward seeping of brines) is common in accumulating evaporite basins (Warren, 2006).

On both magma-poor and magma-rich margins, syn-exhumation salt basins are pre-breakup, so that salt in conjugate margins was originally part of one contiguous basin. The salt becomes separated, forming breakup edges on the conjugate margins (see Pindell & Kennan, 2007; Hudec et al., 2013). Relief on the breakup edge, or outer high, is enhanced by differential loading of salt and/or volcanics (Imbert, 2005; Quirk et al., 2012) and, more importantly, by fault slip on the outer marginal detachment that soles out near the Moho (Pindell et al., 2013). The outer high may comprise normal oceanic crust (e.g. Hudec et al., 2013) or possibly fault blocks of exhumed mantle or lower continental crust (Sibuet & Tucholke, 2013).

Magma-poor margin segments create more accommodation for sedimentation prior to oceanic spreading than magma-rich segments. Whereas magma-rich margins form subaerial highs, presumably due to excess heat and uplift associated with the magmatic event and generation of volcanic flows, magma-poor margins form topographic lows due to the cooling and sinking of initially elevated, exhumed mantle. A lesser degree of serpentinization due to overlying impermeable salt may enhance subsidence since the buoyancy effect would be reduced. The combination of topographically elevated magma-rich segments and subsidence of magma-poor segments provides the accommodation for sag-basin fill and evaporite deposition (Fig. 20c). In other words, the major syn-exhumation salt basins, such as those in the Gulf of Mexico and South Atlantic, formed over magma-poor margin segments, with the salt thinning and onlapping laterally onto the volcanic edifices of magma-rich segments. Salt basins can develop along magma-rich segments such as the eastern margin of the USA and the conjugate margin of NW Africa (e.g. Davison, 2005; Post et al., 2013), but they are typically small basins in local sags or fault-bounded graben within the SDR provinces.

image

Figure 20. Schematic cross-sections (after oceanic spreading and associated subsidence) illustrating relationship of syn-exhumation salt to magma-rich and magma-poor hyperextended margins: (a) magma-poor margin with thick salt basin and presalt sag sequence above hyperextended continental crust and exhumed, serpentinized (diagonal lines) subcontinental mantle; (b) magma-rich margin with thin salt onlapping topographic high of volcanic crust above hyperextended continental crust; (c) strike line showing gradual transition from magma-poor to magma-rich character, with sag basin and salt thinning and onlapping laterally onto volcanic edifice. The transition is more complex than shown, with intrusives and extrusives in the magma-poor segment and possible exhumed mantle in the magma-poor segment. Vertical black dashed lines indicate intersections with other sections.

Download figure to PowerPoint

The major salt basins may be limited along strike by structural highs related to the opening history of the rifted margins. For example, in the Scotian and Moroccan margins, the northern limit of salt beneath the present-day slope was likely the major tectonic boundary between the older Central Atlantic (Nova Scotia and Morocco) and the younger North Atlantic (Newfoundland and Iberia). However, the southern boundaries of both the major Central Atlantic and South Atlantic salt basins are more problematic since rifting and spreading propagated from south to north in both cases (e.g. Schettino & Turco, 2009; Torsvik et al., 2009). If areas to the south were at more advanced stages of separation, what created the barriers that provided basin isolation for evaporite deposition? A simple solution is provided by the transition from northern magma-poor segments to more southerly magma-rich segments (Fig. 20c). In other words, the isolation of the Brazilian and African basins necessary to generate evaporites was provided not so much by a distinct linear ridge (e.g. Davison, 2007; Mohriak et al., 2008; Davison et al., 2012; Quirk et al., 2013) as by the more regional subaerial highs of the Pelotas Basin and Walvis Basin SDR provinces. It was likely marine water percolating through the SDR provinces, not marine water moving through or over an outer volcanic high or brine interaction with underlying volcanics, that led to MgSO4-poor evaporites in the South Atlantic. Finally, the lack of salt in distal settings on the Iberian-Newfoundland margins is probably due to the lack of a volcanic barrier to the south because by the time thinning and hyperextension had ended in the Early Cretaceous, there was already an open ocean just to the south in the Central Atlantic.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References
  1. Passive-margin salt basins can be classified as prerift, syn-stretching, syn-thinning and syn-exhumation based on the four-stage model for hyperextended, magma-poor margins proposed by Péron-Pinvidic & Manatschal (2009). Each type has a distinctive mixture of characteristics ranging from the original areal and thickness distribution to the style of salt tectonics.
  2. Prerift salt is extended along with its substrate and cover, first decoupling the two levels but eventually, depending on evolving salt thickness, linking them on larger stretching faults and especially on thinning and exhumation faults. The base salt develops considerable structural relief and diapirs initiate via thick-skinned extension. Where decoupled, suprasalt deformation is influenced by the ramp-flat geometry of the salt detachment. An example is the Western/Basque Pyrenees and Bay of Biscay, where prerift Upper Triassic salt was subjected to Lower Cretaceous stretching, thinning, and exhumation.
  3. Syn-stretching salt is deposited during margin extension on steeply dipping faults. It is concentrated in proximal areas and its thickness distribution is determined by the rift geometry and modified during ongoing extension. The salt decouples extension of any cover and the substrate, again depending on the evolving thickness. Diapirs are triggered by thick-skinned extension and gravity-driven deformation is rare. The best examples are the conjugate margins of Iberia and Newfoundland, where salt was deposited in proximal Upper Triassic to Lower Jurassic rift basins but not in distal areas where Middle Jurassic to Lower Cretaceous thinning and exhumation were concentrated.
  4. Syn-thinning salt is deposited in a mostly symmetric basin initially centred over the H-block. The base salt develops significant relief due to continuing extension on thinning faults, and the salt is highly attenuated or completely offset on the largest faults. Attenuation also occurs during mantle exhumation as the salt is stretched and thinned over the widening zone of exhumation. Salt deformation is triggered by both thick- and thin-skinned (gravitational) processes and allochthonous nappes may form at the distal toe of the salt. A probable example is the Northern Red Sea, where the base salt unconformably overlies proximal stretching faults but is offset by distal thinning faults, resulting in a ramp-flat décollement that accommodates proximal extension, complex translational geometries, and distal contraction and salt inflation.
  5. Syn-exhumation salt is deposited as part of the sag sequence marking regional subsidence during the exhumation stage, but predates final breakup and accretion of normal oceanic crust. The salt stretches and thins with widening of the ocean–continent transition zone, but there is little relief on the base salt and generally minor, gradual thickness variations. Salt deformation is triggered by basinward gravity gliding and allochthonous salt flows over newly formed oceanic crust. Examples include some of the largest (and most hydrocarbon prolific) salt basins such as those in the South Atlantic and Gulf of Mexico, where the base of autochthonous salt has only local and minor relief. Deformation is dominated by gravitational failure with proximal extension and distal contraction, allochthonous salt is common, and there is a bulk movement of salt basinward.
  6. The major syn-exhumation salt basins of conjugate margins were originally contiguous. They formed on magma-poor margin segments and were bounded in at least one direction by magma-rich SDR provinces. The sag-basin fill and evaporites thinned onto and onlapped the volcanic highs, which separated the basins from marine water. Low basin relief and complete isolation led to the deposition of remarkably pure evaporite sequences with little or no non-evaporite interbeds.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References

I wish to thank many individuals and organizations that have contributed time or data which made this article possible. Conversations with Josep Anton Muñoz, Eduard Roca, Oriol Ferrer, Scott Sumner, Paul Post, Carl Fiduk, Rob Pascoe, and Sujata Venkatraman helped clarify my thinking, and Jürgen Adam and Martin Jackson provided very helpful reviews. Thomas Hearon and Oriol Ferrer helped with drafting of figures and Mike Hudec supplied the base map for the Gulf of Mexico. Dynamic Data Services, Saudi Aramco, and WesternGeco kindly granted permission to show proprietary seismic data; Sujata Venkatraman, Mike Zinger, Robert Tubbs, Carl Fiduk, and Simon Hayter were instrumental in obtaining that permission. The Geomodels Research Institute at the University of Barcelona provided logistical support and the Institute of Tectonic Studies at the University of Texas at El Paso (funded by BP, BHP-Billiton, Chevron, ConocoPhillips, ExxonMobil, and Shell) provided financial support.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Prerift Salt Basins
  5. Syn-Stretching Salt Basins
  6. Syn-Thinning Salt Basins
  7. Syn-Exhumation Salt Basins
  8. Discussion
  9. Conclusions
  10. Acknowledgments
  11. References
  • Alves, T.M., Gawthorpe, R.L., Hunt, D.W. & Monteiro, J.H. (2002) Jurassic tectono-sedimentary evolution of the Northern Lusitanian Basin (offshore Portugal). Mar. Petrol. Geol., 19, 727754.
  • Alves, T.M., Moita, C., Sandnes, F., Cunha, T., Monteiro, J.H. & Pinheiro, L.M. (2006) Mesozoic-Cenozoic evolution of North Atlantic continental-slope basins: the Peniche basin, western Iberian margin. AAPG Bull., 90, 3160.
  • Azevedo, R.L., Gomide, M.J., Viviers, M.C. & Hashimoto, M.T. (1987) Bioestratigrafica do Cretácêo marinho da Bacia de Campos, Brasil. Rev. Brasil. Geocienc., 17, 147153.
  • Balkwill, H.R. & Legall, F.D. (1989) Whale Basin, offshore Newfoundland: extension and salt diapirism. In: Extensional Tectonics and Stratigraphy of the North Atlantic Margins (Ed. by A.J. Tankard & H.R. Balkwill) AAPG Mem., 40, 233245.
  • Barker, S. & Mukherjee, S.S. (2011) Interpretation of the basement step – some observations and implications in the Gulf of Mexico [abs]. AAPG Ann. Conv. Exhib. Abstracts, 13, 13 pp.
  • Blaich, O.A., Faleide, J.I. & Tsikalas, F. (2011) Crustal breakup and continent-ocean transition at South Atlantic conjugate margins. J. Geophys. Res., 116, BO1042, Doi: 10.1029/2010JB007686.
  • Bohannon, R.G., Naeser, C.W., Schmidt, D.L. & Zimmerman, R.A. (1989) The timing of uplift, volcanism, and rifting peripheral to the Red Sea: a case for passive rifting? J. Geophys. Res., 94, 16831701.
  • Boillot, G., Recq, M. & Scientific Party ODP Leg 103 (1987) Tectonic denudation of the upper mantle along passive margins: a model based on drilling results (ODP leg 103, western Galicia margin, Spain). Tectonophysics, 132, 335342.
  • Bosworth, W. (1994) A model for the three-dimensional evolution of continental rift basins, north-east Africa. In: Geology of Northeast Africa (Part 2) (Ed. by H. Schandelmeier & R.J. Stern) Geol. Rundsch., 83, 671688.
  • Bosworth, W., Huchon, P. & McClay, K. (2005) The Red Sea and Gulf of Aden Basins. J. Afr. Earth Sci., 43, 334378.
  • Braun, J. & Beaumont, C. (1989) A physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins. Geology, 17, 760764.
  • Brinkmann, R. & Lögters, H. (1968) Diapirs in western Pyrenees and foreland, Spain. In: Diapirism and Diapirs (Ed. by J. Braunstein & G.D. O'Brien) AAPG Mem., 8, 275292.
  • Brun, J.-P. & Fort, X. (2004) Compressional salt tectonics (Angolan margin). Tectonophysics, 382, 129150.
  • Brun, J.-P. & Fort, X. (2011) Salt tectonics at passive margins: geology versus models. Mar. Petrol. Geol., 28, 11231145.
  • Cartwright, J., Jackson, M.P.A., Higgins, S. & Dooley, T. (2012) Strain partitioning in gravity driven shortening of a thick, multilayered evaporite sequence. In: Salt Tectonics, Sediments, Prospectivity (Ed. by G.I. Alsop, S.G. Archer, A.J. Hartley, N.T. Grant & R. Hodgkinson) Geol. Soc. London Spec. Publ., 363, 329356.
  • Cobbold, P.R. & Szatmari, P. (1991) Radial gravitational gliding on passive margins. Tectonophysics, 187, 249289.
  • Cobbold, P.R., Szatmari, P., Demercian, L.S., Coelho, D. & Rosello, E.A. (1995) Seismic and experimental evidence for thin-skinned horizontal shortening by convergent radial gliding on evaporites, deep-water Santos Basin, Brazil. In: Salt Tectonics: A Global Perspective (Ed. by M.P.A. Jackson, D.G. Roberts & S. Snelson) AAPG Mem., 65, 305321.
  • Cochran, J.R. (1983) A model for development of the Red Sea. AAPG Bull., 67, 4169.
  • Cochran, J.R. & Karner, G.D. (2007) Constraints on the deformation and rupturing of continental lithosphere of the Red Sea: the transition from rifting to drifting. In: Imaging, Mapping and Modelling Continental Lithosphere Extension and Breakup (Ed. by G.D. Karner, G. Manatschal & L.M. Pinheiro) Geol. Soc. London Spec. Publ., 282, 265289.
  • Davison, I. (1999) Tectonics and hydrocarbon distribution along the Brazilian South Atlantic margin. In: Oil and Gas Habitats of the South Atlantic (Ed. by N.R. Cameron, R.H. Bate & V.S. Clure) Geol. Soc. London Spec. Publ., 153, 133151.
  • Davison, I. (2005) Central Atlantic margin basins of North West Africa: geology and hydrocarbon potential (Morocco to Guinea). J. Afr. Earth Sci., 43, 254274.
  • Davison, I. (2007) Geology and tectonics of the South Atlantic Brazilian salt basins. In: Deformation of the Continental Crust: The Legacy of Mike Coward (Ed. by A.C. Ries, R.W.H. Butler & R.H. Graham) Geol. Soc. London Spec. Publ., 272, 345359.
  • Davison, I., Anderson, L. & Nuttall, P. (2012) Salt deposition, loading and gravity drainage in the Campos and Santos Salt basins. In: Salt Tectonics, Sediments, Prospectivity (Ed. by G.I. Alsop, S.G. Archer, A.J. Hartley, N.T. Grant & R. Hodgkinson) Geol. Soc. London Spec. Publ., 363, 157172.
  • Demercian, S., Szatmari, P. & Cobbold, P.R. (1993) Style and pattern of salt diapirs due to thin-skinned gravitational gliding, Campos and Santos basins, offshore Brazil. Tectonophysics, 228, 393433.
  • Dercourt, J., Ricou, L.E. & Vrielynck, B., Eds. (1993) Atlas Tethys Paleoenvironmental Maps. Gauthier-Villars, Paris.
  • Diegel, F.A., Karlo, J.F., Schuster, D.C., Shoup, R.C. & Tauvers, P.R. (1995) Cenozoic structural evolution and tectono-stratigraphic framework of the northern Gulf Coast continental margin. In: Salt Tectonics: A Global Perspective (Ed. by M.P.A. Jackson, D.G. Roberts & S. Snelson) AAPG Mem., 65, 109151.
  • Dooley, T.P., Jackson, M.P.A. & Hudec, M.R. (2013) Coeval extension and shortening above and below salt canopies on an uplifted, divergent, continental margin: the northern Gulf of Mexico. AAPG Bull., Doi: 1306/03271312072. (in press)
  • Duval, B., Cramez, C. & Jackson, M.P.A. (1992) Raft tectonics in the Kwanza Basin, Angola. Mar. Petrol. Geol., 9, 389404.
  • Evans, R. (1978) Origin and significance of evaporites in basins around Atlantic margin. AAPG Bull., 62, 223234.
  • Ferrer, O., Roca, E., Benjumea, B., Muñoz, J.A., Ellouz, N. & Marconi Team (2008) The deep seismic reflection MARCONI-3 profile: role of extensional Mesozoic structure during the Pyrenean contractional deformation at the eastern part of the Bay of Biscay. Mar. Petrol. Geol., 25, 714730.
  • Ferrer, O., Jackson, M.P.A., Roca, E. & Rubinat, M. (2012) Evolution of salt structures during extension and inversion of the offshore Parentis Basin (Eastern Bay of Biscay). In: Salt Tectonics, Sediments, Prospectivity (Ed. by G.I. Alsop, S.G. Archer, A.J. Hartley, N.T. Grant & R. Hodgkinson) Geol. Soc. London Spec. Publ., 363, 361379.
  • Fiduk, J.C. & Rowan, M.G. (2012) Analysis of folding and deformation within layered evaporites in Blocks BM-S-8 & -9, Santos Basin, Brazil. In: Salt Tectonics, Sediments, Prospectivity (Ed. by G.I. Alsop, S.G. Archer, A.J. Hartley, N.T. Grant & R. Hodgkinson) Geol. Soc. London Spec. Publ., 363, 471487.
  • Florineth, D. & Froitzheim, N. (1994) Transition from continental to oceanic basement in the Tasna nappe (Engadine window, Graubünden, Switzerland): evidence for Early Cretaceous opening of the Valais ocean. Schweiz. Mineral. Petrogr. Mitt., 74, 437448.
  • Fonck, J.-M., Cramez, C. & Jackson, M.P.A. (1998) Role of subaerial volcanic rocks and major unconformities in the creation of South Atlantic margins [abs]. AAPG Int. Conf. Extended Abstracts, 3839.
  • Fort, X. & Brun, J.-P. (2012) Kinematics of regional salt flow in the northern Gulf of Mexico. In: Salt Tectonics, Sediments, Prospectivity (Ed. by G.I. Alsop, S.G. Archer, A.J. Hartley, N.T. Grant & R. Hodgkinson) Geol. Soc. London Spec. Publ., 363, 265287.
  • Fort, X., Brun, J.-P. & Chauvel, F. (2004) Salt tectonics on the Angolan margin, synsedimentary deformation processes. AAPG Bull., 88, 15231544.
  • Froitzheim, N. & Eberli, G.P. (1990) Extensional detachment faulting in the evolution of a Tethys passive continental margin, eastern Alps, Switzerland. GSA Bull., 102, 12971308.
  • Gamboa, L.A.P., Machado, M.A.P., Da Silveira, D.P., De Freitas, J.T.R. & Da Silva, S.R.P. (2008) Evaporitos estratificados no Atlântico Sul: interpretação sísmica e controle tectono-estratigráfico na Bacia de Santos. In: Sal: Geologia e Tectônica, Exemplos nas Basicas Brasileiras (Ed. by W. Mohriak, P. Szatmari & S.M.C. Anjos), pp. 340359. Beca Ediçôes Ltda, São Paulo.
  • Geoffroy, L. (2005) Volcanic passive margins. CR Geosci., 337, 13951408.
  • Gibbs, A.D. (1984) Structural evolution of extensional basin margins. J. Geol. Soc. London, 141, 609620.
  • Heaton, R.C., Jackson, M.P.A., Bamahmoud, M. & Nani, A.S.O. (1995) Superposed Neogene extension, contraction, and salt canopy emplacement in the Yemeni Red Sea. In Salt Tectonics: A Global Perspective (Ed. by M.P.A. Jackson, D.G. Roberts & S. Snelson) AAPG Mem., 65, 333351.
  • Henry, S.G., Brumbaugh, W. & Cameron, N. (1995) Presalt source rock development on Brazil's conjugate margin: West African examples [abs]. 1st Latin Am. Geophys. Conf. Extended Abstracts, 3, 13.
  • Henry, P., Azambre, R., Montigny, R., Rossy, M. & Stevenson, R.K. (1998) Late mantle evolution of the Pyrenean sub-continental lithospheric mantle in the light of new 40Ar-39Ar and Sm-Nd ages on pyroxenites and peridotites (Pyrenees, France). Tectonophysics, 296, 103123.
  • Henry, S., Danforth, A., Venkatraman, S. & Willacy, C. (2004) PSDM subsalt imaging reveals new insights into petroleum systems and plays in Angola-Congo-Gabon [abs]. Petrol. Explorer. Soc. Gr. Br.–Houston Geol. Soc. Joint Afr. Symp.
  • Hite, R.J. & Buckner, D.H. (1981) Stratigraphic correlations, facies concepts, and cyclicity in Pennsylvanian rocks of the Paradox Basin. In: Geology of the Paradox Basin (Ed. by D.L. Wiegand), pp. 147159. Rocky Mtn. Assoc. Geol., Denver.
  • Hubbard, R.J. (1988) Age and significance of sequence boundaries on Jurassic and Early Cretaceous rifted continental margins. AAPG Bull., 72, 4972.
  • Hudec, M.R. & Jackson, M.P.A. (2004) Regional restoration across the Kwanza Basin, Angola: salt tectonics triggered by repeated uplift of a metastable passive margin. AAPG Bull., 88, 971990.
  • Hudec, M.R. & Peel, F.J. (2010) Influence of basement structure on evolution of the deepwater Gulf of Mexico [abs]. AAPG Ann. Conv. Exhib. Abstracts, 19, 166117.
  • Hudec, M.R., Norton, I.O., Jackson, M.P.A. & Peel, F.J. (2013) Jurassic evolution of the Gulf of Mexico Salt Basin. AAPG Bull., Doi: 10.1306/04011312073. (in press)
  • Hughes, G.W. & Johnson, R.S. (2005) Lithostratigraphy of the Red Sea. GeoArabia, 10, 49126.
  • Hughes, G.W., Abdine, S. & Girgis, M.H. (1992) Miocene biofacies development and geological history of the Gulf of Suez, Egypt. Mar. Petrol. Geol., 9, 228.
  • Huismans, R. & Beaumont, C. (2011) Depth-dependent extension, two-stage breakup and cratonic underplating at rifted margins. Nature, 473, 7478.
  • Imbert, P. (2005) The Mesozoic opening of the Gulf of Mexico: part 1, evidence for oceanic accretion during and after salt deposition. In: Petroleum Systems of Divergent Continental Margin Basins (Ed. by P.J. Post, N.C. Rosen, D.L. Olson, S.L. Palmes, K.T. Lyons & G.B. Newton), pp. 11191150. 25th Annual GCSSEPM Foundation Bob F. Perkins Research Conference, Houston.
  • Imbert, P. & Philippe, Y. (2005) The Mesozoic opening of the Gulf of Mexico: part 2, integrating seismic and magnetic data into a general opening model. In: Petroleum Systems of Divergent Continental Margin Basins (Ed. by P.J. Post, N.C. Rosen, D.L. Olson, S.L. Palmes, K.T. Lyons & G.B. Newton), pp. 11511189. 25th Annual GCSSEPM Foundation Bob F. Perkins Research Conference, Houston.
  • Jackson, M.P.A. & Hudec, M.R. (2005) Stratigraphic record of translation down ramps in a passive-margin salt detachment. J. Struct. Geol., 27, 889911.
  • Jackson, M.P.A. & Vendeville, B.C. (1994) Regional extension as a geologic trigger for diapirism. Geol. Soc. Am. Bull., 106, 5773.
  • Jackson, M.P.A., Cramez, C. & Fonck, J.-M. (2000) Role of subaerial volcanic rocks and mantle plumes in creation of South Atlantic margins: implications for salt tectonics and source rocks. Mar. Petrol. Geol., 17, 477498.
  • Jackson, M.P.A., Dooley, T.P., Hudec, M.R. & Mcdonnell, A.I. (2011) The pillow fold belt: a key subsalt structural province in the northern Gulf of Mexico. AAPG Search Discov. Article (#10329)
  • Jammes, S., Manatschal, G., Lavier, L. & Masini, E. (2009) Tectono-sedimentary evolution related to extreme crustal thinning ahead of a propagating ocean: the example of the western Pyrenees. Tectonics, 28, TC4012.
  • Jammes, S., Manatschal, G. & Lavier, L. (2010) Interaction between prerift salt and detachment faulting in hyperextended rift systems: the example of the Parentis and Mauléon basins (Bay of Biscay and western Pyrenees). AAPG Bull., 94, 957975.
  • Karner, G.D. & Driscoll, N.W. (2000) Style, timing and distribution of tectonic deformation across the Exmouth Plateau, northwest Australia, determined from stratal architecture and quantitative basin modelling. In: Continental Tectonics (Ed. by N.R. Cameron, R.H. Bate & V.S. Clure) Geol. Soc. London Spec. Publ., 164, 271311.
  • Karner, G.D. & Gamboa, L.A.P. (2007) Timing and origin of the South Atlantic pre-salt sag basins and their capping evaporites. In: Evaporites through Space and Time (Ed. by B.C. Schreiber, S. Lugli & M. Bąbel) Geol. Soc. London Spec. Publ., 285, 1535.
  • Karner, G.D., Driscoll, N.W. & Barker, H.N. (2003) Syn-rift regional subsidence across the West African continental margin: the role of lower plate ductile extension. In: Petroleum Geology of Africa: New Themes and Developing Technologies (Ed. by T.J. Arthur, D.S. MacGregor & N.R. Cameron) Geol. Soc. London Spec. Publ., 207, 105129.
  • Kneller, E.A. & Johnson, C.A. (2011) Plate kinematics of the Gulf of Mexico based on integrated observations from the Central and South Atlantic. Gulf Coast Assoc. Geol. Soc. Trans., 61, 283299.
  • Krawsczyk, C.M., Reston, T.J., Beslier, M.-O. & Boillot, G. (1996) Evidence for detachment tectonics on the Iberia abyssal plain rifted margin. In: Proceedings of the Ocean Drilling Program, Scientific Results (Ed. by R.G. Whitmarsh, D.S. Sawyer, A. Klaus & D.G. Masson), Ocean Drilling Program, College Station, TX, 149, 603615.
  • Labails, C., Olivet, J.-L., Aslanian, D. & Roest, W.R. (2010) An alternative early opening scenario for the Central Atlantic Ocean. Earth Planet. Sci. Lett., 297, 355368.
  • Lavier, L. & Manatschal, G. (2006) A mechanism to thin the continental lithosphere at magma-poor margins. Nature, 440, 324328.
  • Le Pichon, X. & Francheteau, J. (1978) A plate tectonic analysis of the Red Sea–Gulf of Aden area. Tectonophysics, 46, 369406.
  • Lemoine, M., Bas, T., Arnaud-Vanneau, A., Arnaud, H., Gidon, M., Bourdon, M., Graciansky, P.C., Rudkievicz, J.L., Megard-Galli, J. & Tricart, P. (1986) The continental margin of the Mesozoic Tethys in the Western Alps. Mar. Petrol. Geol., 3, 179199.
  • Lentini, M.R., Fraser, S.I., Sumner, H.S. & Davies, R.J. (2010) Geodynamics of the central South Atlantic conjugate margins: implications for hydrocarbon potential. Petrol. Geosci., 16, 217229.
  • Louden, K., Wu, Y. & Tari, G. (2013) Systematic variations in basement morphology and rifting geometry along the Nova Scotia and Morocco conjugate margins. In: Conjugate Divergent Margins (Ed. by W.U. Mohriak, A. Danforth, P.J. Post, D.E. Brown, G.C. Tari, M. Nemčok & S.T. Sinha) Geol. Soc. London Spec. Publ., 369, 267287.
  • Manatschal, G. (2004) New models for evolution of magma-poor rifted margins based on a review of data and concepts from West Iberia and the Alps. Int. J. Earth Sci., 93, 432466.
  • Manatschal, G. & Karner, G.D. (2012) Inter-relationship between tectonic and magmatic processes leading to continental breakup at hyper-extended rifted margins [abs]. Deep-Water Continental Margins, 44. Geological Society, London.
  • Mann, J. & Rigg, J.W.D. (2012) New geological insights into the Santos Basin. GeoExpro, 9, 3640.
  • Marton, L.G., Tari, G.C. & Lehmann, C.T. (2000) Evolution of the Angolan passive margin, West Africa, with emphasis on post-salt structural styles. In: Atlantic Rifts and Continental Margins (Ed. by W. Mohriak & M. Talwani) Am. Geophys. Union Geophys. Monogr., 115, 129149.
  • McKenzie, D. (1978) Some remarks on the development of sedimentary basins. Earth Planet. Sci. Lett., 40, 2532.
  • Meisling, K.E., Cobbold, P.R. & Mount, V.S. (2001) Segmentation of an obliquely rifted margin, Campos and Santos basins, southeastern Brazil. AAPG Bull., 85, 19031924.
  • Mickus, K., Stern, R.J., Keller, G.R. & Anthony, E.Y. (2009) Potential field evidence for a volcanic rifted margin along the Texas Gulf Coast. Geology, 37, 387390.
  • Miranda, L.R., Cardenas, A., Maldonado, R., Reyes, E., Ruiz, J. & Williams, C. (2013) Play hipotetico pre-sal en augas profundas del Golfo de Mexico. Congreso Mexicano del Petroleo 2013, digital extended abstracts.
  • Mitchell, N.C., Ligi, M., Ferrante, V., Bonatti, E. & Rutter, E. (2010) Submarine salt flows in the central Red Sea. GSA Bull., 122, 701713.
  • Mohn, G., Manatschal, G., Müntener, O., Beltrando, M. & Masini, E. (2010) Unraveling the interaction between tectonic and sedimentary processes during lithospheric thinning in the Alpine Tethys margins. Int. J. Earth Sci., Doi: 10.1007/s00531-010-0566-6.
  • Mohriak, W.U. & LeRoy, S. (2013) Architecture of rifted continental margins and break-up evolution: insights from the South Atlantic, North Atlantic and Red Sea–Gulf of Aden conjugate margins. In: Conjugate Divergent Margins (Ed. by W.U. Mohriak, A. Danforth, P.J. Post, D.E. Brown, G.C. Tari, M. Nemčok & S.T. Sinha) Geol. Soc. London Spec. Publ., 369, 497535.
  • Mohriak, W.U., Macedo, J.M., Castellani, R.T., Rangel, H.D., Barros, A.Z.N., Latgé, M.A.L., Ricci, J.A., Mizusaki, A.M.P., Szatmari, P., Demercian, L.S., Rizzo, J.G. & Aires, J.R. (1995) Salt tectonics and structural styles in the deep-water province of the Cabo Frio region, Rio de Janeiro, Brazil. In: Salt Tectonics: A Global Perspective (Ed. by M.P.A. Jackson, D.G. Roberts & S. Snelson) AAPG Mem., 65, 273304.
  • Mohriak, W.U., Bassetto, M. & Vieira, I.S. (1998) Crustal architecture and tectonic evolution of the Sergipe-Alagoas and Jacuípe basins, offshore northeastern Brazil. Tectonophysics, 288, 199220.
  • Mohriak, W.U., Nemčok, M. & Enciso, G. (2008) South Atlantic divergent margin evolution: rift-border uplift and salt tectonics in the basins of SE Brazil. In: West Gondwana Pre-Cenozoic Correlations across the South Atlantic Region (Ed. by R.J. Pankhurst, R.A.J. Trouw, B.B. Brito Neves & M.J. de Wit) Geol. Soc. London Spec. Publ., 294, 365398.
  • Mohriak, W.U., Cunha Filho, C.A., Vicentini, A.G. & Gomes, A.L. (2010) Modelo geofisico de ruptura continental em bacia evaporitica: o caso hitórico do Mar Vermelho. Simpósio de Geofisica da Petrobras, Boletim de Resumos Expandidos. Angro dos Reis, Brazil.
  • Mougenot, C. & Al-Shakhis, A.A. (1999) Depth imaging sub-salt structures: a case study in the Midyan Peninsula. GeoArabia, 4, 335463.
  • Mutter, J.C., Talwani, M. & Stoffa, P.L. (1982) Origin of seaward-dipping reflectors in oceanic crust off the Norwegian margin by “subaerial sea-floor spreading”. Geology, 10, 353357.
  • Peel, F.J., Travis, C.J. & Hossack, J.R. (1995) Genetic structural provinces and salt tectonics of the Cenozoic offshore U.S. Gulf of Mexico: a preliminary analysis. In: Salt Tectonics: A Global Perspective (Ed. by M.P.A. Jackson, D.G. Roberts & S. Snelson) AAPG Mem., 65, 153175.
  • Pérez-Gussinyé, M. (2013) A tectonic model for hyperextension at magma-poor rifted margins: an example from the West Iberia – Newfoundland conjugate margins. In: Conjugate Divergent Margins (Ed. by W.U. Mohriak, A. Danforth, P.J. Post, D.E. Brown, G.C. Tari, M. Nemčok & S.T. Sinha) Geol. Soc. London Spec. Publ., 369, 403427.
  • Péron-Pinvidic, G., Gernigon, L., Gaina, C. & Ball, P. (2012) Insights from the Jan Mayen system in the Norwegian–Greenland sea—I. Mapping of a microcontinent. Geophys. J. Int., 191, 385412.
  • Péron-Pinvidic, G. & Manatschal, G. (2009) The final rifting evolution at deep magma-poor passive margins from Iberia-Newfoundland: a new point of view. Int. J. Earth Sci., 98, 15811597.
  • Péron-Pinvidic, G. & Manatschal, G. (2010) From microcontinents to extensional allochthons: witnesses of how continents rift and break apart? Petrol. Geosci., 16, 189197.
  • Péron-Pinvidic, G., Manatschal, G. & Osmundsen, P.T. (2013) Structural comparison of archetypal Atlantic rifted margins: a review of observations and concepts. Mar. Petrol. Geol., 43, 2147.
  • Péron-Pinvidic, G., Manatschal, G., Minshull, T.A. & Dean, S. (2007) Tectonosedimentary evolution of the deep Iberia-Newfoundland margins: evidence for a complex breakup history. Tectonics, 26, Doi: 10.129/2006TC001970.
  • Pilcher, R.S., Kilsdonk, B. & Trude, J. (2011) Primary basins and their boundaries in the deep-water northern Gulf of Mexico: origin, trap styles, and petroleum system implications. AAPG Bull., 95, 219240.
  • Pindell, J. & Horn, B.W. (2012) Rifting: seismic examples from the western Florida margin and around the world [abs]. AAPG Search Discov. (#90142)
  • Pindell, J. & Kennan, L. (2001) Kinematic evolution of the Gulf of Mexico and Caribbean. In: Petroleum Systems of Deep-Water Basins: Global and Gulf of Mexico Experience (Ed. by R.H. Fillon, N.C. Rosen, P. Weimer, A. Lowrie, H. Pettingill, R.L. Phair, H.H. Roberts & B. van Hoorn), pp. 193220. 21st Annual GCSSEPM Foundation Bob F. Perkins Research Conference, Houston.
  • Pindell, J. & Kennan, L. (2007) Rift models and the salt-cored marginal wedge in the northern Gulf of Mexico: implications for deep-water Paleogene Wilcox deposition and basinwide maturation. In: The Paleogene of the Gulf of Mexico and Caribbean Basins (Ed. by L. Kennan, J. Pindell & N.C. Rosen), 27th Annual GCSSEPM Foundation Bob F. Perkins Research Conference, CD-ROM, Houston.
  • Pindell, J. & Kennan, L. (2009) Tectonic evolution of the Gulf of Mexico, Caribbean and northern South America in the mantle reference frame: an update. In: The Origin and Evolution of the Caribbean Plate (Ed. by K. James, M. Lorente & J. Pindell) Geol. Soc. London Spec. Publ., 328, 155.
  • Pindell, J., Graham, R. & Horn, B. (2013) Rift to drift rapid outer margin tectonic collapse at passive margins, with emphasis on the Gulf of Mexico. Basin Res. (in press)
  • Planke, S., Symonds, P.A., Alvestad, E. & Skogseid, J. (2000) Seismic volcanostratigraphy of large-volume basaltic extrusive complexes on rifted margins. J. Geophys. Res., 105, 1933519351.
  • Post, P.J. (2005) Constraints on the interpretation of the origin and early development of the Gulf of Mexico Basin. In: Petroleum Systems of Divergent Continental Margin Basins (Ed. by P.J. Post, N.C. Rosen, D.L. Olson, S.L. Palmes, K.T. Lyons & G.B. Newton), pp. 10161061. 25th Annual GCSSEPM Foundation Bob F. Perkins Research Conference, Houston.
  • Post, P.J., Elliott, E.T., Klazynski, R.J., Klocek, E.S., Decort, T.M., Riches, T.J. & Li, K. (2013) US Central Atlantic: new plays and petroleum prospectivity. In: Conjugate Divergent Margins (Ed. by W.U. Mohriak, A. Danforth, P.J. Post, D.E. Brown, G.C. Tari, M. Nemčok & S.T. Sinha) Geol. Soc. London Spec. Publ., 369, 323336.
  • Preiss, W.V. (2000) The Adelaide Geosyncline of South Australia and its significance in Neoproterozoic continental reconstruction. Precambrian Res., 100, 2163.
  • Quirk, D.G., Schødt, N., Lassen, B., Ings, S.J., Hsu, D., Hirsch, K.K. & Von Nicolai, C. (2012) Salt tectonics on passive margins: examples from Santos, Campos and Kwanza basins. In: Salt Tectonics, Sediments, Prospectivity (Ed. by G.I. Alsop, S.G. Archer, A.J. Hartley, N.T. Grant & R. Hodgkinson) Geol. Soc. London Spec. Publ., 363, 207244.
  • Quirk, D.G., Hertle, M., Jeppesen, J.W., Raven, M., Mohriak, W.U., Kann, D.J., Nørgaard, M., Howe, M.J., Hsu, D., Coffey, B. & Mendes, M.P. (2013) Rifting, subsidence and continental break-up above a mantle plume in the central South Atlantic. In: Conjugate Divergent Margins (Ed. by W.U. Mohriak, A. Danforth, P.J. Post, D.E. Brown, G.C. Tari, M. Nemčok & S.T. Sinha) Geol. Soc. London Spec. Publ., 369, 185214.
  • Ranero, C.R. & Pérez-Gussinyé, M. (2010) Sequential faulting explains the asymmetry and extension discrepancy of conjugate margins. Nature, 468, 294299.
  • Rasmussen, E.S., Lomholt, S., Andersen, C. & Vejbæk, O.V. (1998) Aspects of the structural evolution of the Lusitanian basin in Portugal and the shelf and slope area offshore Portugal. Tectonophysics, 300, 199255.
  • Reston, T.J. (1996) The S reflector west of Galicia: the seismic signature of a detachment fault. Geophys. J. Int., 127, 230244.
  • Reston, T.J. (2009) The structure, evolution and symmetry of the magma-poor rifted margins of the North and Central Atlantic: a synthesis. Tectonophysics, 468, 627.
  • Richardson, M. & Arthur, M.A. (1988) The Gulf of Suez–northern Red Sea Neogene rift: a quantitative basin analysis. Mar. Petrol. Geol., 5, 245270.
  • Roberts, M., Hollister, C., Yarger, H. & Welch, R. (2005) Regional geologic and geophysical observations basinward of the Sigsbee escarpment and Mississippi Fan Fold Belt, central deep-water Gulf of Mexico: hydrocarbon prospectivity and play types. In: Petroleum Systems of Divergent Continental Margin Basins (Ed. by P.J. Post, N.C. Rosen, D.L. Olson, S.L. Palmes, K.T. Lyons & G.B. Newton), pp. 11901199. 25th Annual GCSSEPM Foundation Bob F. Perkins Research Conference, Houston.
  • Roca, E., Muñoz, J.A., Ferrer, O. & Ellouz, N. (2011) The role of the Bay of Biscay Mesozoic extensional structure in the configuration of the Pyrenean orogen: constraints from the MARCONI deep seismic reflection survey. Tectonics, 30, Doi: 10.1029/2010TC002735.
  • Roeser, H.A. (1975) A detailed magnetic survey of the southern Red Sea. Geol. Jb, 13, 131153.
  • Rowan, M.G. & Inman, K. (2006) Shallow and deep structural provinces of the northern Gulf of Mexico [abs]. AAPG Annual Meeting, Search Discov., Houston. (#90052)
  • Rowan, M.G., Peel, F.J. & Vendeville, B.C. (2004) Gravity-driven foldbelts on passive margins. In: Thrust Tectonics and Hydrocarbon Systems (Ed. by K.R. McClay) AAPG Mem., 82, 157182.
  • Rowan, M.G., Hutton, B., Sandberg, A., Anderson, D. & Mozer, E. (2009) Central Louisiana deepwater: salt architecture and depositional patterns. AAPG Ann. Conv. Exhib. Abstracts, 18, 181.
  • Rowan, M.G., Peel, F.J., Vendeville, B.C. & Gaullier, V. (2012a) Salt tectonics at passive margins: geology versus models – discussion. Mar. Petrol. Geol., 37, 184194.
  • Rowan, M.G., Sumner, H.S., Huston, H., Venkatraman, S. & Dunbar, D. (2012b) Constraining interpretations of the crustal architecture of the Northern Gulf of Mexico. Gulf Coast Assoc. Geol. Soc., 62, 605608.
  • Salvador, A. (1987) Late Triassic-Jurassic paleogeography and origin of the Gulf of Mexico basin. AAPG Bull., 71, 419451.
  • Salvador, A. (1991) Origin and development of the Gulf of Mexico basin. In: The Gulf of Mexico Basin (Ed. by A. Salvador) Geol. NA, v. J., 389444. Geological Society of America, Boulder.
  • Schettino, A. & Turco, E. (2009) Breakup of Pangaea and plate kinematics of the Central Atlantic and Atlas regions. Geophys. J. Int., 178, 10781097.
  • Shillington, D.J., Holbrook, W.S., Tucholke, B.E., Hopper, J.R., Louden, K.E., Larsen, H.C., Van Avendonk, H.J.A., Deemer, S. & Hall, J. (2004) Data report: marine geophysical data on the Newfoundland nonvolcanic rifted margin around SCREECH Transect 2. Proc. ODP Init. Rep, 103, 317.
  • Sibuet, J.-C. & Tucholke, B.E. (2013) The geodynamic province of transitional lithosphere adjacent to magma-poor continental margins. In: Conjugate Divergent Margins (Ed. by W.U. Mohriak, A. Danforth, P.J. Post, D.E. Brown, G.C. Tari, M. Nemčok & S.T. Sinha) Geol. Soc. London Spec. Publ., 369, 429452.
  • Sibuet, J.-C., Srivastava, S.P., Enachescu, M. & Karner, G.D. (2007) Early Cretaceous motion of Flemish Cap with respect to North America: implications on the formation of Orphan Basin and SE Flemish Cap – Galicia Bank conjugate margins. In: Imaging, Mapping and Modelling Continental Lithosphere Extension and Breakup (Ed. by G.D. Karner, G. Manatschal & L.M. Pinheiro) Geol. Soc. London Spec. Publ., 282, 6376.
  • Stewart, S.A. & Clarke, J.A. (1999) Impact of salt on the structure of the Central North Sea hydrocarbon fairways. In: Petroleum Geology of Northwest Europe: Proceedings of the 5th Conference (Ed. A.J. Fleet & S.A.R. Boldy), pp. 179200. Geological Society, London.
  • Sutra, E. & Manatschal, G. (2012) How does the continental crust thin in a hyperextended rifted margin? Insights from the Iberia margin. Geology, 40, 139142.
  • Talwani, M. & Abreu, V. (2000) Inferences regarding initiation of oceanic crust formation from the U.S. East Coast margin and conjugate South Atlantic margins. In: Atlantic Rifts and Continental Margins (Ed. by W. Mohriak & M. Talwani) Am. Geophys. Union Geophys. Monogr., 115, 211233.
  • Tankard, A.J., Welsink, H.J. & Jenkins, W.A.M. (1989) Structural styles and stratigraphy of the Jeanne d'Arc Basin, Grand Banks of Newfoundland. In: Extensional Tectonics and Stratigraphy of the North Atlantic Margins (Ed. by A.J. Tankard & H.R. Balkwill) AAPG Mem., 40, 265282.
  • Tari, G., Molnar, J. & Ashton, P. (2003) Examples of salt tectonics from west Africa: a comparative approach. In: Petroleum Geology of Africa: New Themes and Developing Technologies (Ed. by T.J. Arthur, D.S. MacGregor & N.R. Cameron) Geol. Soc. London Spec. Publ., 207, 85104.
  • Tari, G., Brown, D., Jabour, H., Hafid, M., Louden, K. & Zizi, M. (2012) The conjugate margins of Morocco and Nova Scotia. In: Regional Geology and Tectonics: Phanerozoic Passive Margins, Cratonic Basins and Global Tectonic Maps (Ed. by D.G. Roberts & A.W. Bally), pp. 285323. Elsevier, Amsterdam.
  • Taylor, B., Goodliffe, A.M. & Martinez, F. (1999) How continents break up: insights from Papua New Guinea. J. Geophys. Res., 104, 74797521.
  • Torsvik, T.H., Rousse, S., Labails, C. & Smethurst, M. (2009) A new scheme for the opening of the South Atlantic Ocean and the dissection of an Aptian salt basin. Geophys. J. Int., 177, 13151333.
  • Tubbs, R.E., Jr, Aly, H.G., Afifi, A.M., Raterman, N.S., Kaream, Y.K. & Hughes, G.W. (2013) A brief geologic history of the Midyan area: northern Red Sea, Kingdom of Saudi Arabia. GeoArabia. (in press)
  • Tucholke, B.E., Sawyer, D.S. & Sibuet, J.-C. (2007) Breakup of the Newfoundland – Iberia rift. In: Imaging, Mapping and Modelling Continental Lithosphere Extension and Breakup (Ed. by G.D. Karner, G. Manatschal & L.M. Pinheiro) Geol. Soc. London Spec. Publ., 282, 946.
  • Unternehr, P., Péron-Pinvidic, G., Manatschal, G. & Sutra, E. (2010) Hyper-extended crust in the South Atlantic: in search of a model. Petrol. Geosci., 16, 207215.
  • Van Avendonk, H.J.A., Holbrook, W.S., Nunes, G.T., Shillington, D.J., Tucholke, B.E. & Louden, K.E., Louden, K.E., Larsen, H.C. & Hopper, J.R. (2006) Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada. J. Geophys. Res., 111, Doi: 10.1029/2005JB004156.
  • Vendeville, B.C. & Jackson, M.P.A. (1992a) The rise of diapirs during thin-skinned extension. Mar. Petrol. Geol., 9, 331353.
  • Vendeville, B.C. & Jackson, M.P.A. (1992b) The fall of diapirs during thin-skinned extension. Mar. Petrol. Geol., 9, 354371.
  • Voggenreiter, W., Hotzl, H. & Mechie, J. (1988) Low-angle detachment origin for the development of the Red Sea? Tectonics, 150, 5175.
  • Warren, J. (2006) Evaporites: Sediments, Resources and Hydrocarbons. Springer, Berlin.
  • Wernicke, B. (1981) Low-angle normal faults in the Basin and Range province: nappe tectonics in an extending orogen. Nature, 291, 645648.
  • Whitmarsh, R.B., Manatschal, G. & Minshull, T.A. (2001) Evolution of magma-poor continental margins from rifting to seafloor spreading. Nature, 413, 150154.
  • Withjack, M.O. & Callaway, S. (2000) Active normal faulting beneath a salt layer: an experimental study of deformation patterns in the cover sequence. AAPG Bull., 84, 627651.
  • Worrall, D.M. & Snelson, S. (1989) Evolution of the northern Gulf of Mexico, with emphasis on Cenozoic growth faulting and the role of salt. In: The Geology of North America: An Overview (Ed. by A.W. Bally & A.R. Palmer) Geol. NA, v. A., 97138. Geological Society of America, Boulder.
  • Wu, Y., Louden, K.E., Funck, T., Jackson, H.R. & Dehler, S.A. (2006) Crustal structure of the central Nova Scotia margin off Eastern Canada. Geophys. J. Int., 166, 878906.
  • Zalan, P.V., Severino, M.D.C.G., Rigoti, C.A., Magnavita, L.P., De Oliveira, J.A.B. & Vianna, A.R. (2011) An entirely new 3D-view of the crustal and mantle structure of a South Atlantic passive margin – Santos, Campos and Espírito Santo basins, Brazil. Search Discov. (#30177)
  • Ziegler, P.A. (1988) Evolution of the Arctic–North Atlantic and the Western Tethys. AAPG Memoir 43.